Module org.eclipse.persistence.core
Package org.eclipse.persistence.queries

Class QueryByExamplePolicy

java.lang.Object
org.eclipse.persistence.queries.QueryByExamplePolicy
All Implemented Interfaces:
Serializable
public class QueryByExamplePolicy extends Object implements Serializable

Purpose: This policy defines the configuration options for a Query By Example query.

Description: A Query By Example query is an ObjectLevelReadQuery where the selection criteria is built from an example domain object passed in via setExampleObject.

If no policy is specified the selection criteria is built from the example object in the following way:

  • Attributes of the example object set to null are ignored.
  • Attributes set to the default value for their primitive type (such as 0 for int) are ignored.
  • Unmapped attributes are ignored.
  • A domain object is returned by the query only if its values for all the included attributes equal those set in the example object.

A policy can be set on the query to:

  • Always consider an attribute even if set to null or the default value for its type. See alwaysIncludeAttribute.
  • Ignore attributes set to some other special value. See excludeValue.
  • Match a null attribute on the example object with domain objects that have either null for that attribute also, or have set a meaningful (notNull) value for that attribute. See setShouldUseEqualityForNulls(boolean).
  • Use specialized operations when comparing attributes set in the example object with those set in the domain objects. Matching attributes can be those with values greater than, less than, like, or not equal to that set in the example object. See addSpecialOperation(java.lang.Class<?>, java.lang.String).

Note: When setting an attribute on the example object which is itself a java object with an ObjectReferenceMapping, the mapped components of that attribute will be considered, not the entire object. There is no limit to how many mapped objects can be nested inside the example object.

Note: setExampleObject is different from setSelectionObject in ReadObjectQuery which reads a single object by first extracting the primary key from the selection object.

Restrictions:

  • Only attributes whose mappings are DirectToField, Aggregate (Embeddable), ObjectReference (OneToOne) or Collection type OneToMany/ManyToMany are considered in a Query By Example object. The behaviour when an example object has attribute values for other mappings types is undefined.
    • To ensure the example does not include any unsupported mappings the flag setValidateExample(boolean) should be set to true on the corresponding QueryByExamplePolicy to ensure no unsupported relationship types are used in the example.
    • For OneToMany and ManyToMany mappings the elements within the collections and the references attribute values will be added to the expression as disjuncts (OR)

Example: 

 // This example uses like for Strings and the salary must be greater
 // than zero.
 ReadAllQuery query = new ReadAllQuery();
 Employee employee = new Employee();
 employee.setFirstName("B%");
 employee.setLastName("S%");
 employee.setSalary(0);
 query.setExampleObject(employee);
 QueryByExamplePolicy policy = new QueryByExamplePolicy();
 policy.addSpecialOperation(String.class, "like");
 policy.addSpecialOperation(Integer.class, "greaterThan");
 policy.alwaysIncludeAttribute(Employee.class, "salary");
 query.setQueryByExamplePolicy(policy);
 Vector results = (Vector) session.executeQuery(query);
Since:
TOPLink/Java 3.0
See Also:

  • Field Summary

    Fields
    Modifier and Type
    Field
    Description
    Map
    attributesToAlwaysInclude
     
    boolean
    shouldUseEqualityForNulls
     
    Map
    specialOperations
     
    protected boolean
    validateExample
     
    Map
    valuesToExclude
     

  • Constructor Summary

    Constructors
    Constructor
    Description
    QueryByExamplePolicy()
    PUBLIC: Constructs a default policy equal to that used when no policy is specified.

  • Method Summary

    Modifier and Type
    Method
    Description
    void
    addSpecialOperation(Class<?> attributeValueClass, String operation)
    PUBLIC: Allows operations other than Expression.equal to be used for comparisons.
    void
    alwaysIncludeAttribute(Class<?> exampleClass, String attributeName)
    PUBLIC: Always considers the value for a particular attribute as meaningful in a query by example.
    Expression
    completeExpression(Expression expression, Object attributeValue, Class<?> attributeValueClass)
    INTERNAL: This method is used to determine which operation to use for comparison (equal, or a special operation).
    Expression
    completeExpressionForNull(Expression expression)
    INTERNAL: This method is used when the attribute value is null, but it has to be included at all times.
    void
    excludeDefaultPrimitiveValues()
    PUBLIC: Ignores attributes set to the default value for their primitive type.
    void
    excludeValue(boolean value)
    PUBLIC: An attribute in the example object set to an excluded value will be ignored in a Query By Example.
    void
    excludeValue(byte value)
    PUBLIC: An attribute in the example object set to an excluded value will be ignored in a Query By Example.
    void
    excludeValue(char value)
    PUBLIC: An attribute in the example object set to an excluded value will be ignored in a Query By Example.
    void
    excludeValue(double value)
    PUBLIC: An attribute in the example object set to an excluded value will be ignored in a Query By Example.
    void
    excludeValue(float value)
    PUBLIC: An attribute in the example object set to an excluded value will be ignored in a Query By Example.
    void
    excludeValue(int value)
    PUBLIC: An attribute in the example object set to be an excluded value will be ignored in a Query By Example.
    void
    excludeValue(long value)
    PUBLIC: An attribute in the example object set to an excluded value will be ignored in a Query By Example.
    void
    excludeValue(short value)
    PUBLIC: An attribute in the example object set to an excluded value will be ignored in a Query By Example.
    void
    excludeValue(Object value)
    PUBLIC: An attribute in the example object set to an excluded value will be ignored in a Query By Example.
    Map
    getAttributesToAlwaysInclude()
    PUBLIC: Attributes to always consider even if set to null or an excluded value like 0 or false.
    String
    getOperation(Class<?> aClass)
    INTERNAL: determines which operation to use for comparison.
    Map
    getSpecialOperations()
    PUBLIC: The special operations to use in place of equal.
    Map
    getValuesToExclude()
    PUBLIC: Decides which attributes to ignore based on the values they are set to.
    void
    includeAllValues()
    PUBLIC: Considers all mapped attributes in the example object as meaningful in a Query By Example.
    boolean
    isAlwaysIncluded(Class<?> theClass, String attributeName)
    INTERNAL: returns whether the attributeName is to be always included.
    boolean
    isExcludedValue(Object value)
    INTERNAL: returns if the value is in the values to be excluded automatically.
    void
    removeFromValuesToExclude(Object value)
    PUBLIC: Considers all attributes set to a previously excluded value on the example object.
    void
    setAttributesToAlwaysInclude(Map newAttributesToAlwaysInclude)
    INTERNAL: It is possible to generate a Hashtable (keys are the Class, and values the attribute names) of the attributes to be included at all times (even if the value is null, or the value belongs to the values to be excluced automatically).
    void
    setShouldUseEqualityForNulls(boolean shouldUseEqualityForNulls)
    PUBLIC: Matches an included null attribute in the example object either to objects with that attribute also set to null or to any value other than null.
    void
    setSpecialOperations(Map newOperations)
    PUBLIC: The special operations to use in place of equal.
    void
    setValidateExample(boolean validate)
    PUBLIC: When set to true the example object will be validated for unsupported mapping types.
    void
    setValuesToExclude(Map newValuesToExclude)
    PUBLIC: Decides which attributes to ignore based on the values they are set to.
    boolean
    shouldIncludeInQuery(Class<?> aClass, String attributeName, Object attributeValue)
    INTERNAL: This method determines whether an attribute pair is be included in the query.
    boolean
    shouldUseEqualityForNulls()
    PUBLIC: Matches an included null attribute in the example object either to objects with that attribute also set to null or to any value other than null.
    boolean
    shouldValidateExample()
    PUBLIC: Returns true if the example object used with this policy should be validated for attributes with unsupported mappings.

    Methods inherited from class java.lang.Object

    clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

  • Field Details

    • valuesToExclude

      public Map valuesToExclude

    • attributesToAlwaysInclude

      public Map attributesToAlwaysInclude

    • specialOperations

      public Map specialOperations

    • shouldUseEqualityForNulls

      public boolean shouldUseEqualityForNulls

    • validateExample

      protected boolean validateExample

  • Constructor Details

    • QueryByExamplePolicy

      public QueryByExamplePolicy()
      PUBLIC: Constructs a default policy equal to that used when no policy is specified.

      Sets the default values to be excluded, (that includes 0, false, empty String, etc).

      By default if an attribute is null, and yet has to be included at all times, equality (isNull) is used for the comparison. This is used for searching for an object with a null in a certain field.

      See Also:

  • Method Details

    • addSpecialOperation

      public void addSpecialOperation(Class<?> attributeValueClass, String operation)
      PUBLIC: Allows operations other than Expression.equal to be used for comparisons.

      For example if an attribute of type int is set to x in the example object, normally the query will be on all objects whose attributes are also equal to x. The query could however be all objects whose attributes are not x, greater than x, or even less than or equal to x.

      Any comparison operation in Expression which takes the example attribute as a parameter can be used. A list of supported operations is provided below.

      Note: A special operation can not be used for attributes set to null. The only options are isNull (default) and notNull. See setShouldUseEqualityForNulls(boolean).

      Parameters:
      attributeValueClass - Attribute values of which type, for instance Integer, to apply to. Note for int attributes the class is Integer.class not int.class. This is not the Class of the example object the attribute is an instance variable of.
      operation - Name of method in Expression used
      See Also:

    • alwaysIncludeAttribute

      public void alwaysIncludeAttribute(Class<?> exampleClass, String attributeName)
      PUBLIC: Always considers the value for a particular attribute as meaningful in a query by example.

      Required to override the normal behavior which is to ignore an attribute of the example object if set to null, or an excluded value like 0.

      Example: To find all projects without a budget set budget to 0 in the example object and call alwaysIncludeAttribute(Project.class, "budget") on the policy.

      Parameters:
      exampleClass - The class that the attribute belongs to, normally this is the example class unless using nested QBE.
      attributeName - The name of a mapped attribute.

    • completeExpression

      public Expression completeExpression(Expression expression, Object attributeValue, Class<?> attributeValueClass)
      INTERNAL: This method is used to determine which operation to use for comparison (equal, or a special operation).

    • completeExpressionForNull

      public Expression completeExpressionForNull(Expression expression)
      INTERNAL: This method is used when the attribute value is null, but it has to be included at all times. It determines whether to use isNull, or notNull.

    • excludeDefaultPrimitiveValues

      public void excludeDefaultPrimitiveValues()
      PUBLIC: Ignores attributes set to the default value for their primitive type.

      For instance 0 is used as null for deciding which int attributes of the example object can be ignored in a query by example.

      Called by the constructor.

    • excludeValue

      public void excludeValue(byte value)
      PUBLIC: An attribute in the example object set to an excluded value will be ignored in a Query By Example.

      The default excluded value for byte is 0.

    • excludeValue

      public void excludeValue(char value)
      PUBLIC: An attribute in the example object set to an excluded value will be ignored in a Query By Example.

      The default excluded value for char is ''.

    • excludeValue

      public void excludeValue(double value)
      PUBLIC: An attribute in the example object set to an excluded value will be ignored in a Query By Example.

      The default excluded value for double is 0.0.

    • excludeValue

      public void excludeValue(float value)
      PUBLIC: An attribute in the example object set to an excluded value will be ignored in a Query By Example.

      The default excluded value for float is 0.0f.

    • excludeValue

      public void excludeValue(int value)
      PUBLIC: An attribute in the example object set to be an excluded value will be ignored in a Query By Example.

      The default excluded value for int is 0.

    • excludeValue

      public void excludeValue(long value)
      PUBLIC: An attribute in the example object set to an excluded value will be ignored in a Query By Example.

      The default excluded value for long is 0.

    • excludeValue

      public void excludeValue(Object value)
      PUBLIC: An attribute in the example object set to an excluded value will be ignored in a Query By Example.

      The default excluded value for String is "".

      Note: null is special and always considered an excluded value.

    • excludeValue

      public void excludeValue(short value)
      PUBLIC: An attribute in the example object set to an excluded value will be ignored in a Query By Example.

      The default excluded value for short is 0.

    • excludeValue

      public void excludeValue(boolean value)
      PUBLIC: An attribute in the example object set to an excluded value will be ignored in a Query By Example.

      The default excluded value for boolean is false.

    • getAttributesToAlwaysInclude

      public Map getAttributesToAlwaysInclude()
      PUBLIC: Attributes to always consider even if set to null or an excluded value like 0 or false.
      See Also:

    • getOperation

      public String getOperation(Class<?> aClass)
      INTERNAL: determines which operation to use for comparison.

    • getSpecialOperations

      public Map getSpecialOperations()
      PUBLIC: The special operations to use in place of equal.
      Returns:
      A hashtable where the keys are Class objects and the values are the names of operations to use for attributes of that Class.
      See Also:

    • getValuesToExclude

      public Map getValuesToExclude()
      PUBLIC: Decides which attributes to ignore based on the values they are set to.

      If an attribute of the example domain object is set to one of these values it will be ignored, and not considered in the query.

      Attributes set to excluded values are not always ignored. See alwaysIncludeAttribute.

      Returns:
      valuesToExclude The keys and values are values to exclude (key == value). Primitives are wrapped, so int 0 will be stored as Integer(0).
      See Also:

    • includeAllValues

      public void includeAllValues()
      PUBLIC: Considers all mapped attributes in the example object as meaningful in a Query By Example.

      Note: Even attributes of the example object that are not set, and therefore zero or empty by default, will be included.

      Reverses a previous call to excludeDefaultPrimitiveValues().

    • isAlwaysIncluded

      public boolean isAlwaysIncluded(Class<?> theClass, String attributeName)
      INTERNAL: returns whether the attributeName is to be always included.

    • isExcludedValue

      public boolean isExcludedValue(Object value)
      INTERNAL: returns if the value is in the values to be excluded automatically.

    • removeFromValuesToExclude

      public void removeFromValuesToExclude(Object value)
      PUBLIC: Considers all attributes set to a previously excluded value on the example object.

      Primitive values to be removed must first be wrapped inside an Object.

      Parameters:
      value - No attributes set to value will be excluded from a Query By Example. value.getClass() is a key of the Hashtable returned by getValuesToExclude().

      Note: There is a distinction between an attribute and the value it is set to. An attribute can be included independently of its value with alwaysIncludeAttribute (recommended). It can also be included by making the value it is set to no longer excluded.

      Note: null values are special and will always be excluded.

      See Also:

    • setAttributesToAlwaysInclude

      public void setAttributesToAlwaysInclude(Map newAttributesToAlwaysInclude)
      INTERNAL: It is possible to generate a Hashtable (keys are the Class, and values the attribute names) of the attributes to be included at all times (even if the value is null, or the value belongs to the values to be excluced automatically).

    • setShouldUseEqualityForNulls

      public void setShouldUseEqualityForNulls(boolean shouldUseEqualityForNulls)
      PUBLIC: Matches an included null attribute in the example object either to objects with that attribute also set to null or to any value other than null.

      Set to false to only select objects where certain attributes have been set.

      Example: to find all Employees with an assigned address, set attribute address to null in the example object, call alwaysIncludeAttribute(Employee.class, "address") and then call setShouldUseEqualityForNulls(false).

      Note: Unless an attribute set to null is specifically included, it will not be considered at all in the Query By Example.

      Parameters:
      shouldUseEqualityForNulls - If true (by default) uses isNull else notNull.
      See Also:

    • setSpecialOperations

      public void setSpecialOperations(Map newOperations)
      PUBLIC: The special operations to use in place of equal.
      Parameters:
      newOperations - A hashtable where the keys are Class objects and the values are the names of operations to use for attributes of that Class.
      See Also:

    • setValidateExample

      public void setValidateExample(boolean validate)
      PUBLIC: When set to true the example object will be validated for unsupported mapping types. If you wish these mapping types to be ignored either set this flag to false or add the attribute to the list of ignored attributes in this policy

    • setValuesToExclude

      public void setValuesToExclude(Map newValuesToExclude)
      PUBLIC: Decides which attributes to ignore based on the values they are set to.

      An attribute of the example domain object set to one of these values will be ignored, and not considered in the query.

      Attributes set to excluded values are not always ignored. See alwaysIncludeAttribute.

      Parameters:
      newValuesToExclude - The keys and values are values to exclude (key == value). Primitives are wrapped, so int 0 will be stored as Integer(0).
      See Also:

    • shouldIncludeInQuery

      public boolean shouldIncludeInQuery(Class<?> aClass, String attributeName, Object attributeValue)
      INTERNAL: This method determines whether an attribute pair is be included in the query.

    • shouldUseEqualityForNulls

      public boolean shouldUseEqualityForNulls()
      PUBLIC: Matches an included null attribute in the example object either to objects with that attribute also set to null or to any value other than null.

      Set to false to only select objects where certain attributes have been set.

      Example: to find all Employees with an assigned address, set attribute address to null in the example object, call alwaysIncludeAttribute(Employee.class, "address") and then call setShouldUseEqualityForNulls(false).

      Returns:
      If true (by default) uses isNull else notNull.
      See Also:

    • shouldValidateExample

      public boolean shouldValidateExample()
      PUBLIC: Returns true if the example object used with this policy should be validated for attributes with unsupported mappings.