Package com.google.appengine.api.datastore

Class Query

java.lang.Object
com.google.appengine.api.datastore.Query
All Implemented Interfaces:
Serializable
public final class Query extends Object implements Serializable
Query encapsulates a request for zero or more Entity objects out of the datastore. It supports querying on zero or more properties, querying by ancestor, and sorting. Entity objects which match the query can be retrieved in a single list, or with an unbounded iterator.
See Also:

  • Field Details

  • Constructor Details

    • Query

      public Query()
      Create a new kindless Query that finds Entity objects. Note that kindless queries are not yet supported in the Java dev appserver.

      Currently the only operations supported on a kindless query are filter by __key__, ancestor, and order by __key__ ascending.

    • Query

      public Query(String kind)
      Create a new Query that finds Entity objects with the specified kind. Note that kindless queries are not yet supported in the Java dev appserver.
      Parameters:
      kind - the kind or null to create a kindless query

    • Query

      public Query(Key ancestor)
      Create a new Query that finds Entity objects with the specified Key as an ancestor.
      Parameters:
      ancestor - the ancestor key or null
      Throws:
      IllegalArgumentException - If ancestor is not complete.

    • Query

      public Query(@Nullable String kind, @Nullable Key ancestor)
      Create a new Query that finds Entity objects with the specified kind and the specified ancestor. Note that kindless queries are not yet supported in the Java dev appserver.
      Parameters:
      kind - the kind or null to create a kindless query
      ancestor - the ancestor key or null
      Throws:
      IllegalArgumentException - If the ancestor is not complete.

  • Method Details

    • getKind

      public @Nullable String getKind()
      Only Entity objects whose kind matches this value will be returned.

    • getAppId

      public String getAppId()
      Returns the appId for this Query.

    • getNamespace

      public String getNamespace()
      Returns the namespace for this Query.

    • getAncestor

      public Key getAncestor()
      Gets the current ancestor for this query, or null if there is no ancestor specified.

    • setAncestor

      public Query setAncestor(Key ancestor)
      Sets an ancestor for this query.

      This restricts the query to only return result entities that are descended from a given entity. In other words, all of the results will have the ancestor as their parent, or parent's parent, or etc.

      If null is specified, unsets any previously-set ancestor. Passing null as a parameter does not query for entities without ancestors (this type of query is not currently supported).

      Returns:
      this (for chaining)
      Throws:
      IllegalArgumentException - If the ancestor key is incomplete, or if you try to unset an ancestor and have not set a kind, or if you try to unset an ancestor and have not previously set an ancestor.

    • setDistinct

      public Query setDistinct(boolean distinct)
      Sets whether to return only results with distinct values of the properties being projected.
      Parameters:
      distinct - if this query should be distinct. This may only be used when the query has a projection.
      Returns:
      this (for chaining)

    • getDistinct

      public boolean getDistinct()
      Returns whether this query is distinct.
      See Also:

    • setFilter

      public Query setFilter(@Nullable Query.Filter filter)
      Sets the filter to use for this query.
      Parameters:
      filter - the filter to use for this query, or null
      Returns:
      this (for chaining)
      See Also:

    • getFilter

      public @Nullable Query.Filter getFilter()
      Returns the filter for this query, or null.
      See Also:

    • addFilter

      @Deprecated public Query addFilter(String propertyName, Query.FilterOperator operator, Object value)
      Deprecated.
      Use setFilter(Filter)
      Add a Query.FilterPredicate on the specified property.

      All Query.FilterPredicates added using this message are combined using Query.CompositeFilterOperator.AND.

      Cannot be used in conjunction with setFilter(Filter) which sets a single Query.Filter instead of many Query.FilterPredicates.

      Parameters:
      propertyName - The name of the property to which the filter applies.
      operator - The filter operator.
      value - An instance of a supported datastore type. Note that entities with multi-value properties identified by propertyName will match this filter if the multi-value property has at least one value that matches the condition expressed by operator and value. For more information on multi-value property filtering please see the datastore documentation.
      Returns:
      this (for chaining)
      Throws:
      NullPointerException - If propertyName or operator is null.
      IllegalArgumentException - If value is not of a type supported by the datastore. See DataTypeUtils.isSupportedType(Class). Note that unlike PropertyContainer.setProperty(String, Object), you cannot provide a Collection containing instances of supported types to this method.

    • getFilterPredicates

      @Deprecated public List<Query.FilterPredicate> getFilterPredicates()
      Deprecated.
      Use setFilter(Filter) and getFilter() instead
      Returns a mutable list of the current filter predicates.
      See Also:

    • addSort

      public Query addSort(String propertyName)
      Specify how the query results should be sorted.

      The first call to addSort will register the property that will serve as the primary sort key. A second call to addSort will set a secondary sort key, etc.

      This method will always sort in ascending order. To control the order of the sort, use addSort(String,SortDirection).

      Note that entities with multi-value properties identified by propertyName will be sorted by the smallest value in the list. For more information on sorting properties with multiple values please see the datastore documentation.

      Returns:
      this (for chaining)
      Throws:
      NullPointerException - If any argument is null.

    • addSort

      public Query addSort(String propertyName, Query.SortDirection direction)
      Specify how the query results should be sorted.

      The first call to addSort will register the property that will serve as the primary sort key. A second call to addSort will set a secondary sort key, etc.

      Note that if direction is Query.SortDirection.ASCENDING, entities with multi-value properties identified by propertyName will be sorted by the smallest value in the list. If direction is Query.SortDirection.DESCENDING, entities with multi-value properties identified by propertyName will be sorted by the largest value in the list. For more information on sorting properties with multiple values please see the datastore documentation.

      Returns:
      this (for chaining)
      Throws:
      NullPointerException - If any argument is null.

    • getSortPredicates

      public List<Query.SortPredicate> getSortPredicates()
      Returns a mutable list of the current sort predicates.

    • setKeysOnly

      public Query setKeysOnly()
      Makes this query fetch and return only keys, not full entities.
      Returns:
      this (for chaining)

    • clearKeysOnly

      public Query clearKeysOnly()
      Clears the keys only flag.
      Returns:
      this (for chaining)
      See Also:

    • addProjection

      public Query addProjection(Projection projection)
      Adds a projection for this query.

      Projections are limited in the following ways:

      • Un-indexed properties cannot be projected and attempting to do so will result in no entities being returned.
      • Projection names must be unique.
      • Properties that have an equality filter on them cannot be projected. This includes the operators Query.FilterOperator.EQUAL and Query.FilterOperator.IN.
      Parameters:
      projection - the projection to add
      Returns:
      this (for chaining)
      Throws:
      IllegalArgumentException - if the query already contains a projection with the same name
      See Also:

    • getProjections

      public Collection<Projection> getProjections()
      Returns a mutable collection properties included in the projection for this query.

      If empty, the full or keys only entities are returned. Otherwise partial entities are returned. A non-empty projection is not compatible with setting keys-only. In this case a IllegalArgumentException will be thrown when the query is prepared.

      Projection queries are similar to SQL statements of the form: 

      SELECT prop1, prop2, ...
      As they return partial entities, which only contain the properties specified in the projection. However, these entities will only contain a single value for any multi-valued property and, if a multi-valued property is specified in the order, an inequality property, or the projected properties, the entity will be returned multiple times. Once for each unique combination of values.

      Specifying a projection:

      • May change the type of any property returned in a projection.
      • May change the index requirements for the given query.
      • Will cause a partial entity to be returned.
      • Will cause only entities that contain those properties to be returned.
      However, projection queries are significantly faster than normal queries.
      Returns:
      a mutable collection properties included in the projection for this query
      See Also:

    • isKeysOnly

      public boolean isKeysOnly()
      Returns true if this query will fetch and return keys only, false if it will fetch and return full entities.

    • reverse

      public Query reverse()
      Creates a query sorted in the exact opposite direction as the current one.

      This function requires a sort order on Entity.KEY_RESERVED_PROPERTY to guarantee that each entity is uniquely identified by the set of properties used in the sort (which is required to exactly reverse the order of a query). Advanced users can reverse the sort orders manually if they know the set of sorted properties meets this requirement without a order on Entity.KEY_RESERVED_PROPERTY.

      The results of the reverse query will be the same as the results of the forward query but in reverse direction.

      Cursors from the original query may also be used in the reverse query.

      Returns:
      A new query with the sort order reversed.
      Throws:
      IllegalStateException - if the current query is not sorted by Entity.KEY_RESERVED_PROPERTY.

    • equals

      public boolean equals(@Nullable Object o)
      Overrides:
      equals in class Object

    • hashCode

      public int hashCode()
      Overrides:
      hashCode in class Object

    • toString

      public String toString()
      Outputs a SQL like string representing the query.
      Overrides:
      toString in class Object