org.eclipse.viatra.query.runtime.matchers.backend

## Class QueryEvaluationHint

- java.lang.Object
- - org.eclipse.viatra.query.runtime.matchers.backend.QueryEvaluationHint

-     public class QueryEvaluationHint
      extends java.lang.Object

  Provides VIATRA Query with additional hints on how a query should be evaluated. The same hint can be provided to multiple queries.

  This class is immutable. Overriding options will create a new instance.

  Here be dragons: for advanced users only.

- - ### Nested Class Summary

    Nested Classes
    Modifier and Type | Class and Description
    --- | ---
    `static class` | `QueryEvaluationHint.BackendRequirement`

  - ### Constructor Summary

    Constructors
    Constructor and Description
    `QueryEvaluationHint(java.util.Map<QueryHintOption<?>,java.lang.Object> backendHintSettings, IQueryBackendFactory queryBackendFactory)` Specifies the suggested query backend, and value settings for additional backend-specific options.
    `QueryEvaluationHint(java.util.Map<QueryHintOption<?>,java.lang.Object> backendHintSettings, QueryEvaluationHint.BackendRequirement backendRequirementType)` Specifies the suggested query backend requirements, and value settings for additional backend-specific options.

  - ### Method Summary

    All Methods Instance Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `boolean` | `equals(java.lang.Object obj)`
    `java.util.Map<QueryHintOption<?>,java.lang.Object>` | `getBackendHintSettings()` Each entry in the immutable map overrides backend-specific options regarding query evaluation.
    `IQueryBackendFactory` | `getQueryBackendFactory()` A suggestion for choosing the query evaluator algorithm.
    `QueryEvaluationHint.BackendRequirement` | `getQueryBackendRequirementType()` Returns the backend requirement described by this hint.
    `<HintValue> HintValue` | `getValueOrDefault(QueryHintOption<HintValue> option)` Returns the value of the given hint option from the given hint collection, or the default value if not defined.
    `<HintValue> HintValue` | `getValueOrNull(QueryHintOption<HintValue> option)` Returns the value of the given hint option from the given hint collection, or null if not defined.
    `int` | `hashCode()`
    `boolean` | `isOptionOverridden(QueryHintOption<?> option)` Returns whether the given hint option is overridden.
    `QueryEvaluationHint` | `overrideBy(QueryEvaluationHint overridingHint)` Override values in this hint and return a consolidated instance.
    `java.lang.String` | `toString()`

    - ### Methods inherited from class java.lang.Object

      `clone, finalize, getClass, notify, notifyAll, wait, wait, wait`

- - ### Constructor Detail

    - #### QueryEvaluationHint

          public QueryEvaluationHint(java.util.Map<QueryHintOption<?>,java.lang.Object> backendHintSettings,
                                     QueryEvaluationHint.BackendRequirement backendRequirementType)

      Specifies the suggested query backend requirements, and value settings for additional backend-specific options.

      The backend requirement type must not be `QueryEvaluationHint.BackendRequirement.SPECIFIC` - for that case, use the constructor `QueryEvaluationHint(Map, IQueryBackendFactory)`.

      Parameters:
        `backendHintSettings` - if non-null, each entry in the map overrides backend-specific options regarding query evaluation (null-valued map entries permitted to erase hints); passing null means default options associated with the query
        `backendRequirementType` - defines the kind of backend requirement
      Since:
        2.0

    - #### QueryEvaluationHint

          public QueryEvaluationHint(java.util.Map<QueryHintOption<?>,java.lang.Object> backendHintSettings,
                                     IQueryBackendFactory queryBackendFactory)

      Specifies the suggested query backend, and value settings for additional backend-specific options. The first parameter can be null; if the second parameter is null, it is expected that the other constructor is called instead with a `QueryEvaluationHint.BackendRequirement.UNSPECIFIED` parameter.
      Parameters:
        `backendHintSettings` - if non-null, each entry in the map overrides backend-specific options regarding query evaluation (null-valued map entries permitted to erase hints); passing null means default options associated with the query
        `queryBackendFactory` - overrides the query evaluator algorithm; passing null retains the default algorithm associated with the query
      Since:
        1.5

  - ### Method Detail

    - #### getQueryBackendRequirementType

          public QueryEvaluationHint.BackendRequirement getQueryBackendRequirementType()

      Returns the backend requirement described by this hint. If a specific backend is required, that can be queried by `getQueryBackendFactory()`.
      Since:
        2.0

    - #### getQueryBackendFactory

          public IQueryBackendFactory getQueryBackendFactory()

      A suggestion for choosing the query evaluator algorithm.

      Returns null iff `getQueryBackendRequirementType()` does not return `QueryEvaluationHint.BackendRequirement.SPECIFIC`; in such cases a corresponding default backend is selected inside the engine

    - #### getBackendHintSettings

          public java.util.Map<QueryHintOption<?>,java.lang.Object> getBackendHintSettings()

      Each entry in the immutable map overrides backend-specific options regarding query evaluation.

      The map is non-null, even if empty. Null-valued map entries are also permitted to erase hints via `overrideBy(QueryEvaluationHint)`.

      Since:
        1.5

    - #### overrideBy

          public QueryEvaluationHint overrideBy(QueryEvaluationHint overridingHint)

      Override values in this hint and return a consolidated instance.
      Since:
        1.4

    - #### isOptionOverridden

          public boolean isOptionOverridden(QueryHintOption<?> option)

      Returns whether the given hint option is overridden.
      Since:
        1.5

    - #### getValueOrNull

          public <HintValue> HintValue getValueOrNull(QueryHintOption<HintValue> option)

      Returns the value of the given hint option from the given hint collection, or null if not defined.
      Since:
        1.5

    - #### getValueOrDefault

          public <HintValue> HintValue getValueOrDefault(QueryHintOption<HintValue> option)

      Returns the value of the given hint option from the given hint collection, or the default value if not defined. Intended to be called by backends to find out the definitive value that should be considered.
      Since:
        1.5

    - #### hashCode

          public int hashCode()

      Overrides:
        `hashCode` in class `java.lang.Object`

    - #### equals

          public boolean equals(java.lang.Object obj)

      Overrides:
        `equals` in class `java.lang.Object`

    - #### toString

          public java.lang.String toString()

      Overrides:
        `toString` in class `java.lang.Object`