Class FeatureQuery

Object
Query
FeatureQuery
All Implemented Interfaces:
Serializable, Cloneable, Emptiable
public class FeatureQuery extends Query implements Cloneable, Emptiable, Serializable
Definition of filtering to apply for fetching a subset of Feature­Set. This query mimics SQL SELECT statements using OGC Filter and Expressions. Information stored in this query can be used directly with Stream API.

Terminology

This class uses relational database terminology:
  • A selection is a filter choosing the features instances to include in the subset. In relational databases, a feature instances are mapped to table rows.
  • A projection (not to be confused with map projection) is the set of feature properties to keep. In relational databases, feature properties are mapped to table columns.

Optional values

All aspects of this query are optional and initialized to "none". Unless otherwise specified, all methods accept a null argument or can return a null value, which means "none".
Since:
1.1
See Also:

  • Constructor Details

    • FeatureQuery

      public FeatureQuery()
      Creates a new query applying no filter.

    • FeatureQuery

      public FeatureQuery(FeatureQuery other)
      Creates a new query initialized to the same values than the given query. This is an alternative to the clone() method when the caller wants to change the implementation class.
      Parameters:
      other - the other query from which to copy the configuration.
      Since:
      1.5
      See Also:

  • Method Details

    • isEmpty

      public boolean isEmpty()
      Returns true if this query do not specify any filtering.
      Specified by:
      is­Empty in interface Emptiable
      Returns:
      if this query performs no filtering.
      Since:
      1.5

    • setProjection

      public void setProjection(String... properties)
      Sets the properties to retrieve by their names. This convenience method wraps the given names in Value­Reference expressions without alias and delegates to set­Projection(Named­Expression...).
      Specified by:
      set­Projection in class Query
      Parameters:
      properties - properties to retrieve, or null to retrieve all properties.
      Throws:
      Illegal­Argument­Exception - if the given array is empty of if a property is duplicated.

    • setProjection

      @SafeVarargs public final void setProjection(Expression<? super AbstractFeature, ?>... properties)
      Sets the properties to retrieve, or null if all properties shall be included in the query. This convenience method wraps the given expression in Feature­Query​.Named­Expressions without alias and delegates to set­Projection(Named­Expression...).
      Parameters:
      properties - properties to retrieve, or null to retrieve all properties.
      Throws:
      Illegal­Argument­Exception - if the given array is empty of if a property is duplicated.

    • setProjection

      public void setProjection(FeatureQuery.NamedExpression... properties)
      Sets the properties to retrieve, or null if all properties shall be included in the query. A query column may use a simple or complex expression and an alias to create a new type of property in the returned features.

      This is equivalent to the column names in the SELECT clause of a SQL statement. Subset of columns is called projection in relational database terminology.

      Parameters:
      properties - properties to retrieve, or null to retrieve all properties.
      Throws:
      Illegal­Argument­Exception - if a property or an alias is duplicated.

    • getProjection

      public FeatureQuery.NamedExpression[] getProjection()
      Returns the properties to retrieve, or null if all properties shall be included in the query. This is the expressions specified in the last call to set­Projection(Named­Expression[]). The default value is null.
      Returns:
      properties to retrieve, or null to retrieve all feature properties.

    • setSelection

      public void setSelection(Envelope domain)
      Sets the approximate area of feature instances to include in the subset. This convenience method creates a filter that checks if the bounding box of the feature's "sis:geometry" property interacts with the given envelope.
      Specified by:
      set­Selection in class Query
      Parameters:
      domain - the approximate area of interest, or null if none.

    • setSelection

      public void setSelection(Filter<? super AbstractFeature> selection)
      Sets a filter for trimming feature instances. Features that do not pass the filter are discarded. Discarded features are not counted for the query limit.
      Parameters:
      selection - the filter, or null if none.

    • getSelection

      public Filter<? super AbstractFeature> getSelection()
      Returns the filter for trimming feature instances. This is the value specified in the last call to set­Selection(Filter). The default value is null, which means that no filtering is applied.
      Returns:
      the filter, or null if none.

    • setOffset

      public void setOffset(long skip)
      Sets the number of feature instances to skip from the beginning. Offset and limit are often combined to obtain paging. The offset cannot be negative.

      Note that setting this property can be costly on parallelized streams. See Stream​.skip(long) for more information.

      Parameters:
      skip - the number of feature instances to skip from the beginning.

    • getOffset

      public long getOffset()
      Returns the number of feature instances to skip from the beginning. This is the value specified in the last call to set­Offset(long). The default value is zero, which means that no features are skipped.
      Returns:
      the number of feature instances to skip from the beginning.

    • setUnlimited

      public void setUnlimited()
      Removes any limit defined by set­Limit(long).

    • setLimit

      public void setLimit(long limit)
      Set the maximum number of feature instances contained in the Feature­Set. Offset and limit are often combined to obtain paging.

      Note that setting this property can be costly on parallelized streams. See Stream​.limit(long) for more information.

      Parameters:
      limit - maximum number of feature instances contained in the Feature­Set.

    • getLimit

      public OptionalLong getLimit()
      Returns the maximum number of feature instances contained in the Feature­Set. This is the value specified in the last call to set­Limit(long).
      Returns:
      maximum number of feature instances contained in the Feature­Set, or empty if none.

    • setLinearResolution

      public void setLinearResolution(Quantity<Length> linearResolution)
      Sets the desired spatial resolution of geometries. This property is an optional hint; resources may ignore it.
      Parameters:
      linear­Resolution - desired spatial resolution, or null for full resolution.

    • getLinearResolution

      public Quantity<Length> getLinearResolution()
      Returns the desired spatial resolution of geometries. A null value means that data are queried at their full resolution.
      Returns:
      desired spatial resolution, or null for full resolution.

    • getXPaths

      public Set<String> getXPaths()
      Returns all XPaths used, directly or indirectly, by this query. The XPath values are extracted from all Value­Reference expressions found in the selection and in the projection. The aliases are ignored.

      The elements in the returned set are in no particular order. The set may be empty but never null.

      Returns:
      all XPaths used, directly or indirectly, by this query.
      Since:
      1.5

    • execute

      protected FeatureSet execute(FeatureSet source) throws DataStoreException
      Applies this query on the given feature set. This method is invoked by the default implementation of Feature­Set​.subset(Query). The default implementation executes the query using the default Stream methods. Queries executed by this method may not benefit from accelerations provided for example by databases. This method should be used only as a fallback when the query cannot be executed natively by Feature­Set​.subset(Query).

      The returned Feature­Set does not cache the resulting Feature instances; the query is processed on every call to the Feature­Set​.features(boolean) method.

      Parameters:
      source - the set of features to filter, sort or process.
      Returns:
      a view over the given feature set containing only the filtered feature instances.
      Throws:
      Data­Store­Exception - if an error occurred during creation of the subset.
      Since:
      1.2
      See Also:

    • optimize

      protected void optimize(FeatureSet source) throws DataStoreException
      Optimizes this query before execution. This method is invoked by execute(Feature­Set) on a clone of the user-provided query. The default implementations tries to optimize the selection filter using Optimization. Subclasses can override for modifying the optimization algorithm.
      Parameters:
      source - the set of features given to the execute(Feature­Set) method.
      Throws:
      Data­Store­Exception - if an error occurred during the optimization of this query.
      Since:
      1.5

    • clone

      public FeatureQuery clone()
      Returns a clone of this query.
      Overrides:
      clone in class Object
      Returns:
      a clone of this query.
      See Also:

    • hashCode

      public int hashCode()
      Returns a hash code value for this query.
      Overrides:
      hash­Code in class Object
      Returns:
      a hash value for this query.

    • equals

      public boolean equals(Object obj)
      Compares this query with the given object for equality.
      Overrides:
      equals in class Object
      Parameters:
      obj - the object to compare with this query.
      Returns:
      whether the two objects are equal.

    • toString

      public String toString()
      Returns a textual representation of this query for debugging purposes. The default implementation returns a string that looks like an SQL Select query.
      Overrides:
      to­String in class Object
      Returns:
      textual representation of this query.