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467 lines
21 KiB
ReStructuredText
467 lines
21 KiB
ReStructuredText
.. highlight:: kotlin
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<script type="text/javascript" src="_static/jquery.js"></script>
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<script type="text/javascript" src="_static/codesets.js"></script>
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API: Persistence
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================
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.. contents::
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Corda offers developers the option to expose all or some parts of a contract state to an *Object Relational Mapping*
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(ORM) tool to be persisted in a *Relational Database Management System* (RDBMS).
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The purpose of this, is to assist :doc:`key-concepts-vault`
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development and allow for the persistence of state data to a custom database table. Persisted states held in the
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vault are indexed for the purposes of executing queries. This also allows for relational joins between Corda tables
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and the organization's existing data.
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The Object Relational Mapping is specified using `Java Persistence API <https://en.wikipedia.org/wiki/Java_Persistence_API>`_
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(JPA) annotations. This mapping is persisted to the database as a table row (a single, implicitly structured data item) by the node
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automatically every time a state is recorded in the node's local vault as part of a transaction.
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.. note:: By default, nodes use an H2 database which is accessed using *Java Database Connectivity* JDBC. Any database
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with a JDBC driver is a candidate and several integrations have been contributed to by the community.
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Please see the info in ":doc:`node-database`" for details.
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Schemas
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-------
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Every ``ContractState`` may implement the ``QueryableState`` interface if it wishes to be inserted into a custom table in the node's
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database and made accessible using SQL.
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.. literalinclude:: ../../core/src/main/kotlin/net/corda/core/schemas/PersistentTypes.kt
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:language: kotlin
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:start-after: DOCSTART QueryableState
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:end-before: DOCEND QueryableState
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The ``QueryableState`` interface requires the state to enumerate the different relational schemas it supports, for
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instance in situations where the schema has evolved. Each relational schema is represented as a ``MappedSchema``
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object returned by the state's ``supportedSchemas`` method.
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Nodes have an internal ``SchemaService`` which decides what data to persist by selecting the ``MappedSchema`` to use.
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Once a ``MappedSchema`` is selected, the ``SchemaService`` will delegate to the ``QueryableState`` to generate a corresponding
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representation (mapped object) via the ``generateMappedObject`` method, the output of which is then passed to the *ORM*.
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.. literalinclude:: ../../node/src/main/kotlin/net/corda/node/services/api/SchemaService.kt
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:language: kotlin
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:start-after: DOCSTART SchemaService
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:end-before: DOCEND SchemaService
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.. literalinclude:: ../../core/src/main/kotlin/net/corda/core/schemas/PersistentTypes.kt
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:language: kotlin
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:start-after: DOCSTART MappedSchema
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:end-before: DOCEND MappedSchema
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With this framework, the relational view of ledger states can evolve in a controlled fashion in lock-step with internal systems or other
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integration points and is not dependant on changes to the contract code.
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It is expected that multiple contract state implementations might provide mappings within a single schema.
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For example an Interest Rate Swap contract and an Equity OTC Option contract might both provide a mapping to
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a Derivative contract within the same schema. The schemas should typically not be part of the contract itself and should exist independently
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to encourage re-use of a common set within a particular business area or CorDapp.
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.. note:: It's advisable to avoid cross-references between different schemas as this may cause issues when evolving ``MappedSchema``
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or migrating its data. At startup, nodes log such violations as warnings stating that there's a cross-reference between ``MappedSchema``'s.
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The detailed messages incorporate information about what schemas, entities and fields are involved.
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``MappedSchema`` offer a family name that is disambiguated using Java package style name-spacing derived from the
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class name of a *schema family* class that is constant across versions, allowing the ``SchemaService`` to select a
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preferred version of a schema.
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The ``SchemaService`` is also responsible for the ``SchemaOptions`` that can be configured for a particular
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``MappedSchema``. These allow the configuration of database schemas or table name prefixes to avoid clashes with
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other ``MappedSchema``.
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.. note:: It is intended that there should be plugin support for the ``SchemaService`` to offer version upgrading, implementation
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of additional schemas, and enable active schemas as being configurable. The present implementation does not include these features
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and simply results in all versions of all schemas supported by a ``QueryableState`` being persisted.
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This will change in due course. Similarly, the service does not currently support
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configuring ``SchemaOptions`` but will do so in the future.
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Custom schema registration
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--------------------------
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Custom contract schemas are automatically registered at startup time for CorDapps. The node bootstrap process will scan for states that implement
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the Queryable state interface. Tables are then created as specified by the ``MappedSchema`` identified by each state's ``supportedSchemas`` method.
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For testing purposes it is necessary to manually register the packages containing custom schemas as follows:
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- Tests using ``MockNetwork`` and ``MockNode`` must explicitly register packages using the `cordappPackages` parameter of ``MockNetwork``
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- Tests using ``MockServices`` must explicitly register packages using the `cordappPackages` parameter of the ``MockServices`` `makeTestDatabaseAndMockServices()` helper method.
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.. note:: Tests using the `DriverDSL` will automatically register your custom schemas if they are in the same project structure as the driver call.
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Object relational mapping
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-------------------------
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To facilitate the ORM, the persisted representation of a ``QueryableState`` should be an instance of a ``PersistentState`` subclass,
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constructed either by the state itself or a plugin to the ``SchemaService``. This allows the ORM layer to always
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associate a ``StateRef`` with a persisted representation of a ``ContractState`` and allows joining with the set of
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unconsumed states in the vault.
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The ``PersistentState`` subclass should be marked up as a JPA 2.1 *Entity* with a defined table name and having
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properties (in Kotlin, getters/setters in Java) annotated to map to the appropriate columns and SQL types. Additional
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entities can be included to model these properties where they are more complex, for example collections (:ref:`Persisting Hierarchical Data<persisting-hierarchical-data>`), so
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the mapping does not have to be *flat*. The ``MappedSchema`` constructor accepts a list of all JPA entity classes for that schema in
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the ``MappedTypes`` parameter. It must provide this list in order to initialise the ORM layer.
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Several examples of entities and mappings are provided in the codebase, including ``Cash.State`` and
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``CommercialPaper.State``. For example, here's the first version of the cash schema.
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.. container:: codeset
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.. literalinclude:: ../../finance/contracts/src/main/kotlin/net/corda/finance/schemas/CashSchemaV1.kt
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:language: kotlin
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.. note:: If Cordapp needs to be portable between Corda OS (running against H2) and Corda Enterprise (running against a standalone database),
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consider database vendors specific requirements.
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Ensure that table and column names are compatible with the naming convention of the database vendors for which the Cordapp will be deployed,
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e.g. for Oracle database, prior to version 12.2 the maximum length of table/column name is 30 bytes (the exact number of characters depends on the database encoding).
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Persisting Hierarchical Data
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----------------------------
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You may wish to persist hierarchical relationships within states using multiple database tables
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You may wish to persist hierarchical relationships within state data using multiple database tables. In order to facillitate this, multiple ``PersistentState``
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subclasses may be implemented. The relationship between these classes is defined using JPA annotations. It is important to note that the ``MappedSchema``
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constructor requires a list of *all* of these subclasses.
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An example Schema implementing hierarchical relationships with JPA annotations has been implemented below. This Schema will cause ``parent_data`` and ``child_data`` tables to be
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created.
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.. container:: codeset
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.. sourcecode:: java
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@CordaSerializable
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public class SchemaV1 extends MappedSchema {
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/**
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* This class must extend the MappedSchema class. Its name is based on the SchemaFamily name and the associated version number abbreviation (V1, V2... Vn).
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* In the constructor, use the super keyword to call the constructor of MappedSchema with the following arguments: a class literal representing the schema family,
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* a version number and a collection of mappedTypes (class literals) which represent JPA entity classes that the ORM layer needs to be configured with for this schema.
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*/
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public SchemaV1() {
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super(Schema.class, 1, ImmutableList.of(PersistentParentToken.class, PersistentChildToken.class));
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}
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/**
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* The @entity annotation signifies that the specified POJO class' non-transient fields should be persisted to a relational database using the services
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* of an entity manager. The @table annotation specifies properties of the table that will be created to contain the persisted data, in this case we have
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* specified a name argument which will be used the table's title.
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*/
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@Entity
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@Table(name = "parent_data")
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public static class PersistentParentToken extends PersistentState {
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/**
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* The @Column annotations specify the columns that will comprise the inserted table and specify the shape of the fields and associated
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* data types of each database entry.
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*/
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@Column(name = "owner") private final String owner;
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@Column(name = "issuer") private final String issuer;
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@Column(name = "amount") private final int amount;
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@Column(name = "linear_id") public final UUID linearId;
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/**
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* The @OneToMany annotation specifies a one-to-many relationship between this class and a collection included as a field.
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* The @JoinColumn and @JoinColumns annotations specify on which columns these tables will be joined on.
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*/
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@OneToMany(cascade = CascadeType.PERSIST)
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@JoinColumns({
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@JoinColumn(name = "output_index", referencedColumnName = "output_index"),
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@JoinColumn(name = "transaction_id", referencedColumnName = "transaction_id"),
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})
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private final List<PersistentChildToken> listOfPersistentChildTokens;
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public PersistentParentToken(String owner, String issuer, int amount, UUID linearId, List<PersistentChildToken> listOfPersistentChildTokens) {
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this.owner = owner;
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this.issuer = issuer;
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this.amount = amount;
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this.linearId = linearId;
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this.listOfPersistentChildTokens = listOfPersistentChildTokens;
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}
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// Default constructor required by hibernate.
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public PersistentParentToken() {
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this.owner = "";
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this.issuer = "";
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this.amount = 0;
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this.linearId = UUID.randomUUID();
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this.listOfPersistentChildTokens = null;
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}
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public String getOwner() {
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return owner;
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}
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public String getIssuer() {
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return issuer;
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}
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public int getAmount() {
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return amount;
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}
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public UUID getLinearId() {
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return linearId;
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}
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public List<PersistentChildToken> getChildTokens() { return listOfPersistentChildTokens; }
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}
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@Entity
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@CordaSerializable
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@Table(name = "child_data")
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public static class PersistentChildToken {
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// The @Id annotation marks this field as the primary key of the persisted entity.
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@Id
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private final UUID Id;
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@Column(name = "owner")
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private final String owner;
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@Column(name = "issuer")
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private final String issuer;
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@Column(name = "amount")
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private final int amount;
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/**
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* The @ManyToOne annotation specifies that this class will be present as a member of a collection on a parent class and that it should
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* be persisted with the joining columns specified in the parent class. It is important to note the targetEntity parameter which should correspond
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* to a class literal of the parent class.
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*/
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@ManyToOne(targetEntity = PersistentParentToken.class)
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private final TokenState persistentParentToken;
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public PersistentChildToken(String owner, String issuer, int amount) {
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this.Id = UUID.randomUUID();
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this.owner = owner;
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this.issuer = issuer;
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this.amount = amount;
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this.persistentParentToken = null;
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}
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// Default constructor required by hibernate.
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public PersistentChildToken() {
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this.Id = UUID.randomUUID();
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this.owner = "";
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this.issuer = "";
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this.amount = 0;
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this.persistentParentToken = null;
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}
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public UUID getId() {
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return Id;
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}
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public String getOwner() {
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return owner;
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}
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public String getIssuer() {
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return issuer;
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}
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public int getAmount() {
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return amount;
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}
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public TokenState getPersistentToken() {
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return persistentToken;
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}
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}
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}
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.. sourcecode:: kotlin
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@CordaSerializable
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object SchemaV1 : MappedSchema(schemaFamily = Schema::class.java, version = 1, mappedTypes = listOf(PersistentParentToken::class.java, PersistentChildToken::class.java)) {
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@Entity
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@Table(name = "parent_data")
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class PersistentParentToken(
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@Column(name = "owner")
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var owner: String,
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@Column(name = "issuer")
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var issuer: String,
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@Column(name = "amount")
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var currency: Int,
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@Column(name = "linear_id")
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var linear_id: UUID,
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@JoinColumns(JoinColumn(name = "transaction_id", referencedColumnName = "transaction_id"), JoinColumn(name = "output_index", referencedColumnName = "output_index"))
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var listOfPersistentChildTokens: MutableList<PersistentChildToken>
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) : PersistentState()
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@Entity
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@CordaSerializable
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@Table(name = "child_data")
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class PersistentChildToken(
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@Id
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var Id: UUID = UUID.randomUUID(),
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@Column(name = "owner")
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var owner: String,
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@Column(name = "issuer")
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var issuer: String,
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@Column(name = "amount")
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var currency: Int,
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@Column(name = "linear_id")
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var linear_id: UUID,
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@ManyToOne(targetEntity = PersistentParentToken::class)
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var persistentParentToken: TokenState
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) : PersistentState()
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Identity mapping
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----------------
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Schema entity attributes defined by identity types (``AbstractParty``, ``Party``, ``AnonymousParty``) are automatically
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processed to ensure only the ``X500Name`` of the identity is persisted where an identity is well known, otherwise a null
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value is stored in the associated column. To preserve privacy, identity keys are never persisted. Developers should use
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the ``IdentityService`` to resolve keys from well know X500 identity names.
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.. _jdbc_session_ref:
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JDBC session
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------------
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Apps may also interact directly with the underlying Node's database by using a standard
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JDBC connection (session) as described by the `Java SQL Connection API <https://docs.oracle.com/javase/8/docs/api/java/sql/Connection.html>`_
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Use the ``ServiceHub`` ``jdbcSession`` function to obtain a JDBC connection as illustrated in the following example:
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.. literalinclude:: ../../node/src/test/kotlin/net/corda/node/services/persistence/HibernateConfigurationTest.kt
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:language: kotlin
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:start-after: DOCSTART JdbcSession
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:end-before: DOCEND JdbcSession
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JDBC sessions can be used in flows and services (see ":doc:`flow-state-machines`").
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The following example illustrates the creation of a custom Corda service using a ``jdbcSession``:
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.. literalinclude:: ../../docs/source/example-code/src/main/kotlin/net/corda/docs/kotlin/vault/CustomVaultQuery.kt
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:language: kotlin
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:start-after: DOCSTART CustomVaultQuery
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:end-before: DOCEND CustomVaultQuery
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which is then referenced within a custom flow:
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.. literalinclude:: ../../docs/source/example-code/src/main/kotlin/net/corda/docs/kotlin/vault/CustomVaultQuery.kt
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:language: kotlin
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:start-after: DOCSTART TopupIssuer
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:end-before: DOCEND TopupIssuer
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For examples on testing ``@CordaService`` implementations, see the oracle example :doc:`here <oracles>`.
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JPA Support
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-----------
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In addition to ``jdbcSession``, ``ServiceHub`` also exposes the Java Persistence API to flows via the ``withEntityManager``
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method. This method can be used to persist and query entities which inherit from ``MappedSchema``. This is particularly
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useful if off-ledger data must be maintained in conjunction with on-ledger state data.
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.. note:: Your entity must be included as a mappedType as part of a ``MappedSchema`` for it to be added to Hibernate
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as a custom schema. If it's not included as a mappedType, a corresponding table will not be created. See Samples below.
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The code snippet below defines a ``PersistentFoo`` type inside ``FooSchemaV1``. Note that ``PersistentFoo`` is added to
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a list of mapped types which is passed to ``MappedSchema``. This is exactly how state schemas are defined, except that
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the entity in this case should not subclass ``PersistentState`` (as it is not a state object). See examples:
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.. container:: codeset
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.. sourcecode:: java
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public class FooSchema {}
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public class FooSchemaV1 extends MappedSchema {
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FooSchemaV1() {
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super(FooSchema.class, 1, ImmutableList.of(PersistentFoo.class));
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}
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@Entity
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@Table(name = "foos")
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class PersistentFoo implements Serializable {
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@Id
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@Column(name = "foo_id")
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String fooId;
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@Column(name = "foo_data")
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String fooData;
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}
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}
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.. sourcecode:: kotlin
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object FooSchema
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object FooSchemaV1 : MappedSchema(schemaFamily = FooSchema.javaClass, version = 1, mappedTypes = listOf(PersistentFoo::class.java)) {
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@Entity
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@Table(name = "foos")
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class PersistentFoo(@Id @Column(name = "foo_id") var fooId: String, @Column(name = "foo_data") var fooData: String) : Serializable
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}
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Instances of ``PersistentFoo`` can be manually persisted inside a flow as follows:
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.. container:: codeset
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.. sourcecode:: java
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PersistentFoo foo = new PersistentFoo(new UniqueIdentifier().getId().toString(), "Bar");
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serviceHub.withEntityManager(entityManager -> {
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entityManager.persist(foo);
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return null;
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});
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.. sourcecode:: kotlin
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val foo = FooSchemaV1.PersistentFoo(UniqueIdentifier().id.toString(), "Bar")
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serviceHub.withEntityManager {
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persist(foo)
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}
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And retrieved via a query, as follows:
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.. container:: codeset
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.. sourcecode:: java
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node.getServices().withEntityManager((EntityManager entityManager) -> {
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CriteriaQuery<PersistentFoo> query = entityManager.getCriteriaBuilder().createQuery(PersistentFoo.class);
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Root<PersistentFoo> type = query.from(PersistentFoo.class);
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query.select(type);
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return entityManager.createQuery(query).getResultList();
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});
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.. sourcecode:: kotlin
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val result: MutableList<FooSchemaV1.PersistentFoo> = services.withEntityManager {
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val query = criteriaBuilder.createQuery(FooSchemaV1.PersistentFoo::class.java)
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val type = query.from(FooSchemaV1.PersistentFoo::class.java)
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query.select(type)
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createQuery(query).resultList
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}
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Please note that suspendable flow operations such as:
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* ``FlowSession.send``
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* ``FlowSession.receive``
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* ``FlowLogic.receiveAll``
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* ``FlowLogic.sleep``
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* ``FlowLogic.subFlow``
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Cannot be used within the lambda function passed to ``withEntityManager``.
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