Package org.eclipse.persistence.internal.expressions

Class FunctionExpression

    • Constructor Detail

      • FunctionExpression

        public FunctionExpression()

    • Method Detail

      • equals

        public boolean equals​(Object object)
        INTERNAL: Return if the expression is equal to the other. This is used to allow dynamic expression's SQL to be cached. This must be over written by each subclass.
        Overrides:
        equals in class Expression

      • computeHashCode

        public int computeHashCode()
        INTERNAL: Compute a consistent hash-code for the expression. This is used to allow dynamic expression's SQL to be cached.
        Overrides:
        computeHashCode in class Expression

      • addChild

        public void addChild​(Expression child)

      • asOf

        public Expression asOf​(AsOfClause clause)
        Description copied from class: Expression
        Sets all tables represented by this expression to be queried as of a past time.

        Example: 

          EclipseLink: employee.asOf(new AsOfClause(pastTime))
  Java: None
  SQL (Flashback): SELECT ... FROM EMPLOYEE AS OF TIMESTAMP (pastTime) t0 ...
  SQL (Generic): .. WHERE (t1.START <= pastTime) AND ((t1.END IS NULL) OR t1.END > pastTime)

        Set an as of clause at the expression level to still query for current objects while expressing selection criteria like:

        • query objects as of one time that met some condition at another time.
        • query objects that changed a certain way over a certain interval (querying for change).

        Simultaneously querying on two versions of the same object (one past one present) lets you express these advanced selection criteria.

        Example: Querying on past attributes using parallel expressions. 

           // Finds all employees who lived in Ottawa as of a past time.
   ExpressionBuilder employee = new ExpressionBuilder();
   ExpressionBuilder pastEmployee = new ExpressionBuilder(Employee.class);
   pastEmployee.asOf(pastTime);
   Expression pastAddress = pastEmployee.get("address"); // by default address will also be as of past time.
   Expression selectionCriteria = pastAddress.get("city").equal("Ottawa").and(
       employee.equal(pastEmployee));

        The advantage of the parallel expression is that you can still read current objects, the as of clause will affect only the where clause / selection criteria.

        You may be tempted to rewrite the above as employee.get("address").asOf(pastTime). That is allowed but see below for the finer points involved in this.

        Example: Querying on object changes using parallel expressions. 

           // Finds all employees who recently received a raise.  Note that current
   // objects are returned, so can be cached normally.
   ExpressionBuilder employee = new ExpressionBuilder();
   Expression pastEmployee = new ExpressionBuilder(Employee.class);
   pastEmployee.asOf(yesterday);
   Expression parallelJoin = employee.equal(pastEmployee);
   Expression selectionCriteria = parallelJoin.and(
       employee.get("salary").greaterThan(pastEmployee.get("salary")));

        Example: Querying on object changes using custom query keys 

           // First define the custom query key and add it to your descriptor.
   ExpressionBuilder builder = new ExpressionBuilder(Employee.class);
   Expression joinCriteria = builder.getField("EMPLOYEE.EMP_ID").equal(builder.getParameter("EMPLOYEE.EMP_ID"));
   OneToOneQueryKey selfReferential = new OneToOneQueryKey();
   selfReferential.setName("this");
   selfReferential.setJoinCriteria(joinCriteria);
   selfReferential.setReferenceClass(Employee.class);
   getSession().getDescriptor(Employee.class).addQueryKey(selfReferential);

   // Now build query as before.
   Expression employee = new ExpessionBuilder();
   Expression pastEmployee = employee.get("this").asOf(yesterday);
   Expression selectionCriteria = employee.get("salary").greaterThan(pastEmployee.get("salary"));

        Note in general that any parallel expression can be rewritten using a custom query key. EclipseLink will even automatically interpret x.get("this") for you so you do not need to define the above query key first.

        Full Reference:

        If an object is mapped to multiple tables, then each table will be as of the same time. Two objects mapped to the same table can not have different as of times. Conversely only expressions which have associated tables can have an as of clause.

        If an as of clause is not explicitly set an expression will use the clause of its base expression, and so on recursively until one is found or an ExpressionBuilder is reached. Some usage scenarios follow:

        • employee.asOf(pastTime).anyOf("projects"): projects as of past time.
        • expressionBuilder.asOf(pastTime): entire expression as of past time.
        • employee.asOf(pastTime).anyOf("projects").asOf(null): projects as of current time.
        • employee.anyOf("projects").asOf(pastTime): projects only as of past time.

        Watch out for x.asOf(oneTime).get("y").asOf(anotherTime).

        • emp.anyOf("phoneNumbers").asOf(yesterday) = emp.asOf(yesterday).anyOf("phoneNumbers") but:
        • emp.get("address").asOf(yesterday) != emp.asOf(yesterday).get("address").
        Whether the join is also as of yesterday depends on which table the foreign key field resides on. In an anyOf the foreign key is always on the right, but in a get (1-1) it could be on either side. For this reason employee.get("address").asOf(yesterday) is undefined as it can mean either 'my address as of yesterday', or 'my address, as of yesterday.'
        Overrides:
        asOf in class Expression
        Parameters:
        clause - A read only data object used to represent a past time.
        Returns:
        this
        See Also:
        AsOfClause, Expression.hasAsOfClause(), Session.acquireHistoricalSession(org.eclipse.persistence.history.AsOfClause), ObjectLevelReadQuery.setAsOfClause(org.eclipse.persistence.history.AsOfClause)

      • doesConform

        public boolean doesConform​(Object object,
                           AbstractSession session,
                           AbstractRecord translationRow,
                           int valueHolderPolicy,
                           boolean isObjectUnregistered)
        INTERNAL: Check if the object conforms to the expression in memory. This is used for in-memory querying. If the expression in not able to determine if the object conform throw a not supported exception.
        Overrides:
        doesConform in class Expression
        isObjectUnregistered - true if object possibly not a clone, but is being conformed against the unit of work cache; if object is not in the UOW cache but some of its attributes are, use the registered versions of object's attributes for the purposes of this method.

      • getFields

        public List<DatabaseField> getFields()
        INTERNAL: Not to be confused with the public getField(String) This returns a collection of all fields associated with this object. Really only applies to query keys representing an object or to expression builders.
        Overrides:
        getFields in class Expression

      • getResultType

        public Class getResultType()

      • hasResultType

        public boolean hasResultType()

      • initializePlatformOperator

        public void initializePlatformOperator​(DatabasePlatform platform)
        INTERNAL:

      • isObjectComparison

        protected boolean isObjectComparison()
        INTERNAL: Return if the represents an object comparison.

      • normalize

        public Expression normalize​(ExpressionNormalizer normalizer)
        INTERNAL: Normalize into a structure that is printable. Also compute printing information such as outer joins. This checks for object isNull, notNull, in and notIn comparisons.
        Overrides:
        normalize in class Expression

      • postCopyIn

        protected void postCopyIn​(Map alreadyDone)
        INTERNAL: Used for cloning.
        Overrides:
        postCopyIn in class BaseExpression

      • resetPlaceHolderBuilder

        public void resetPlaceHolderBuilder​(ExpressionBuilder queryBuilder)
        INTERNAL: Search the tree for any expressions (like SubSelectExpressions) that have been built using a builder that is not attached to the query. This happens in case of an Exists call using a new ExpressionBuilder(). This builder needs to be replaced with one from the query.
        Overrides:
        resetPlaceHolderBuilder in class BaseExpression

      • setLocalBase

        public void setLocalBase​(Expression exp)
        Description copied from class: Expression
        INTERNAL: Set the local base expression, ie the one on the other side of the operator Most types will ignore this, since they don't need it.
        Overrides:
        setLocalBase in class Expression

      • setResultType

        public void setResultType​(Class resultType)

      • twistedForBaseAndContext

        public Expression twistedForBaseAndContext​(Expression newBase,
                                           Expression context,
                                           Expression oldBase)
        INTERNAL: Rebuild myself against the base, with the values of parameters supplied by the context expression. This is used for transforming a standalone expression (e.g. the join criteria of a mapping) into part of some larger expression. You normally would not call this directly, instead calling twist See the comment there for more details"
        Overrides:
        twistedForBaseAndContext in class Expression

      • valueFromObject

        public Object valueFromObject​(Object object,
                              AbstractSession session,
                              AbstractRecord translationRow,
                              int valueHolderPolicy,
                              boolean isObjectUnregistered)
        INTERNAL: Return the value for in memory comparison. This is only valid for valueable expressions.
        Overrides:
        valueFromObject in class Expression
        isObjectUnregistered - true if object possibly not a clone, but is being conformed against the unit of work cache.

      • prepareObjectAttributeCount

        public void prepareObjectAttributeCount​(ExpressionNormalizer normalizer,
                                        ReportItem item,
                                        ReportQuery query,
                                        Map clonedExpressions)
        INTERNAL: JPQL allows count([distinct] e), where e can be an object, not just a single field, however the database only allows a single field, so object needs to be translated to a single field. If the descriptor has a single pk, it is used, otherwise any pk is used if distinct, otherwise a subselect is used. If the object was obtained through an outer join, then the subselect also will not work, so an error is thrown.