Corda has been architected from the ground up to encourage usage of industry standard, proven query frameworks and libraries for accessing RDBMS backed transactional stores (including the Vault).
Corda provides a number of flexible query mechanisms for accessing the Vault:
- Vault Query API
- custom JPA_/JPQL_ queries
- custom 3rd party Data Access frameworks such as `Spring Data <http://projects.spring.io/spring-data>`_
The majority of query requirements can be satisfied by using the Vault Query API, which is exposed via the ``VaultQueryService`` for use directly by flows:
The ``QueryCriteria`` interface provides a flexible mechanism for specifying different filtering criteria, including and/or composition and a rich set of operators to include: binary logical (AND, OR), comparison (LESS_THAN, LESS_THAN_OR_EQUAL, GREATER_THAN, GREATER_THAN_OR_EQUAL), equality (EQUAL, NOT_EQUAL), likeness (LIKE, NOT_LIKE), nullability (IS_NULL, NOT_NULL), and collection based (IN, NOT_IN).
There are four implementations of this interface which can be chained together to define advanced filters.
1.``VaultQueryCriteria`` provides filterable criteria on attributes within the Vault states table: status (UNCONSUMED, CONSUMED), state reference(s), contract state type(s), notaries, soft locked states, timestamps (RECORDED, CONSUMED).
.. note:: Sensible defaults are defined for frequently used attributes (status = UNCONSUMED, includeSoftlockedStates = true).
2.``FungibleAssetQueryCriteria`` provides filterable criteria on attributes defined in the Corda Core ``FungibleAsset`` contract state interface, used to represent assets that are fungible, countable and issued by a specific party (eg. ``Cash.State`` and ``CommodityContract.State`` in the Corda finance module). Filterable attributes include: participants(s), owner(s), quantity, issuer party(s) and issuer reference(s).
.. note:: All contract states that extend the ``FungibleAsset`` now automatically persist that interfaces common state attributes to the **vault_fungible_states** table.
3.``LinearStateQueryCriteria`` provides filterable criteria on attributes defined in the Corda Core ``LinearState`` and ``DealState`` contract state interfaces, used to represent entities that continuously supercede themselves, all of which share the same *linearId* (eg. trade entity states such as the ``IRSState`` defined in the SIMM valuation demo). Filterable attributes include: participant(s), linearId(s), dealRef(s).
.. note:: All contract states that extend ``LinearState`` or ``DealState`` now automatically persist those interfaces common state attributes to the **vault_linear_states** table.
4.``VaultCustomQueryCriteria`` provides the means to specify one or many arbitrary expressions on attributes defined by a custom contract state that implements its own schema as described in the api-persistence_ documentation and associated examples. Custom criteria expressions are expressed using one of several type-safe ``CriteriaExpression``: BinaryLogical, Not, ColumnPredicateExpression. The ColumnPredicateExpression allows for specification arbitrary criteria using the previously enumerated operator types. Furthermore, a rich DSL is provided to enable simple construction of custom criteria using any combination of ``ColumnPredicate``.
..note:: It is a requirement to register any custom contract schemas to be used in Vault Custom queries in the associated `CordaPluginRegistry` configuration for the respective CorDapp using the ``requiredSchemas`` configuration field (which specifies a set of `MappedSchema`)
..note:: Custom contract states that implement the ``Queryable`` interface may now extend common schemas types ``FungiblePersistentState`` or, ``LinearPersistentState``. Previously, all custom contracts extended the root ``PersistentState`` class and defined repeated mappings of ``FungibleAsset`` and ``LinearState`` attributes. See ``SampleCashSchemaV2`` and ``DummyLinearStateSchemaV2`` as examples.
..note:: When specifying the Contract Type as a parameterised type to the QueryCriteria in Kotlin, queries now include all concrete implementations of that type if this is an interface. Previously, it was only possible to query on Concrete types (or the universe of all Contract States).
The Vault Query API leverages the rich semantics of the underlying JPA Hibernate_ based Persistence_ framework adopted by Corda.
..note:: Permissioning at the database level will be enforced at a later date to ensure authenticated, role-based, read-only access to underlying Corda tables.
..note:: API's now provide ease of use calling semantics from both Java and Kotlin. However, it should be noted that Java custom queries are significantly more verbose due to the use of reflection fields to reference schema attribute types.
..note:: Current queries by ``Party`` specify the ``AbstractParty`` which may be concrete or anonymous. In the later case, where an anonymous party does not have an associated X500Name, then no query results will ever be produced. For performance reasons, queries do not use PublicKey as search criteria. Ongoing design work on identity manangement is likely to enhance identity based queries (including composite key criteria selection).
**Dynamic queries** (also using ``VaultQueryCriteria``) are an extension to the snapshot queries by returning an additional ``QueryResults`` return type in the form of an ``Observable<Vault.Update>``. Refer to `ReactiveX Observable <http://reactivex.io/documentation/observable.html>`_ for a detailed understanding and usage of this type.
For advanced use cases that require sophisticated pagination, sorting, grouping, and aggregation functions, it is recommended that the CorDapp developer utilise one of the many proven frameworks that ship with this capability out of the box. Namely, implementations of JPQL (JPA Query Language) such as **Hibernate** for advanced SQL access, and **Spring Data** for advanced pagination and ordering constructs.
The Corda Tutorials provide examples satisfying these additional Use Cases:
1. Template / Tutorial CorDapp service using Vault API Custom Query to access attributes of IOU State
2. Template / Tutorial CorDapp service query extension executing Named Queries via JPQL_
3.`Advanced pagination <https://docs.spring.io/spring-data/commons/docs/current/api/org/springframework/data/repository/PagingAndSortingRepository.html>`_ queries using Spring Data JPA_
Here follows a selection of the most common upgrade scenarios:
1. ServiceHub usage to obtain Unconsumed states for a given contract state type
Previously:
..container:: codeset
..sourcecode:: kotlin
val yoStates = b.vault.unconsumedStates<Yo.State>()
This query returned an ``Iterable<StateAndRef<T>>``
Now:
..container:: codeset
..sourcecode:: kotlin
val yoStates = b.vault.queryBy<Yo.State>().states
The query returns a ``Vault.Page`` result containing:
- states as a ``List<StateAndRef<T : ContractState>>`` sized according to the default Page specification of ``DEFAULT_PAGE_NUM`` (0) and ``DEFAULT_PAGE_SIZE`` (200).
- states metadata as a ``List<Vault.StateMetadata>`` containing Vault State metadata held in the Vault states table.
- the ``PagingSpecification`` used in the query
- a ``total`` number of results available. This value can be used issue subsequent queries with appropriately specified ``PageSpecification`` (according to your paging needs and/or maximum memory capacity for holding large data sets). Note it is your responsibility to manage page numbers and sizes.
2. ServiceHub usage obtaining linear heads for a given contract state type
Previously:
..container:: codeset
..sourcecode:: kotlin
val iouStates = serviceHub.vaultService.linearHeadsOfType<IOUState>()
val iouToSettle = iouStates[linearId] ?: throw Exception("IOUState with linearId $linearId not found.")
Now:
..container:: codeset
..sourcecode:: kotlin
val criteria = QueryCriteria.LinearStateQueryCriteria(linearId = listOf(linearId))
val iouStates = serviceHub.vaultService.queryBy<IOUState>(criteria).states
val iouToSettle = iouStates.singleOrNull() ?: throw Exception("IOUState with linearId $linearId not found.")
3. RPC usage was limited to using the ``vaultAndUpdates`` RPC method, which returned a snapshot and streaming updates as an Observable.
In many cases, queries were not interested in the streaming updates.
Previously:
..container:: codeset
..sourcecode:: kotlin
val iouStates = services.vaultAndUpdates().first.filter { it.state.data is IOUState }
