public abstract Class CompoundExpression

Overrides org.eclipse.persistence.expressions.Expression.aliasForTable.

INTERNAL: Find the alias for a given table from the first or second child in the additionalOuterJoinCriteria

Annotations

@Override

Overrides org.eclipse.persistence.expressions.Expression.asOf.

Doc from org.eclipse.persistence.expressions.Expression.asOf.

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").

Parameters

clause:AsOfClause

A read only data object used to represent a past time.

Returns:Expression

this

Annotations

@Override

Overrides org.eclipse.persistence.expressions.Expression.computeHashCode.

INTERNAL: Compute a consistent hash-code for the expression. This is used to allow dynamic expression's SQL to be cached.

Annotations

@Override

Overrides org.eclipse.persistence.expressions.Expression.create.

INTERNAL:

Annotations

@Override

Overrides org.eclipse.persistence.expressions.Expression.create.

INTERNAL:

Annotations

@Override

Overrides org.eclipse.persistence.expressions.Expression.descriptionOfNodeType.

INTERNAL: Used for debug printing.

Annotations

@Override

Overrides org.eclipse.persistence.expressions.Expression.equals.

INTERNAL: Return if the expression is equal to the other. This is used to allow dynamic expression's SQL to be cached.

Parameters

object:Object

Doc from java.lang.Object.equals.

the reference object with which to compare.

Returns:boolean

Doc from java.lang.Object.equals.

true if this object is the same as the obj argument; false otherwise.

Annotations

@Override

Implements abstract org.eclipse.persistence.expressions.Expression.getBuilder.

Return the expression builder which is the ultimate base of this expression, or null if there isn't one (shouldn't happen if we start from a root)

Annotations

@Override

Overrides org.eclipse.persistence.expressions.Expression.getOperator.

Doc from org.eclipse.persistence.expressions.Expression.getOperator.

INTERNAL: Most expression have operators, so this is just a convenience method.

Annotations

@Override

INTERNAL:

Overrides org.eclipse.persistence.expressions.Expression.isCompoundExpression.

Doc from org.eclipse.persistence.expressions.Expression.isCompoundExpression.

INTERNAL:

Annotations

@Override

Overrides org.eclipse.persistence.expressions.Expression.iterateOn.

INTERNAL: For iterating using an inner class

Annotations

@Override

Overrides org.eclipse.persistence.expressions.Expression.normalize.

INTERNAL: Normalize into a structure that is printable. Also compute printing information such as outer joins.

Annotations

@Override

Overrides org.eclipse.persistence.expressions.Expression.printJava.

INTERNAL: Print java for project class generation

Annotations

@Override

Implements abstract org.eclipse.persistence.expressions.Expression.printSQL.

INTERNAL: Print SQL

Annotations

@Override

Implements abstract org.eclipse.persistence.expressions.Expression.rebuildOn.

INTERNAL: This expression is built on a different base than the one we want. Rebuild it and return the root of the new tree

Annotations

@Override

Implements abstract org.eclipse.persistence.expressions.Expression.resetPlaceHolderBuilder.

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.

Annotations

@Override

Overrides org.eclipse.persistence.expressions.Expression.shallowClone.

INTERNAL: Clear the builder when cloning.

Annotations

@Override

Overrides org.eclipse.persistence.expressions.Expression.twistedForBaseAndContext.

INTRENAL: Used to change an expression off of one base to an expression off of a different base. i.e. expression on address to an expression on an employee's address.

Annotations

@Override

Overrides org.eclipse.persistence.expressions.Expression.validateNode.

Do any required validation for this node. Throw an exception if it's incorrect. Ensure that both sides are not data expressions.

Annotations

@Override

Overrides org.eclipse.persistence.expressions.Expression.writeDescriptionOn.

INTERNAL: Used to print a debug form of the expression tree.

Annotations

@Override

Overrides org.eclipse.persistence.expressions.Expression.writeSubexpressionsTo.

INTERNAL: Used for toString for debugging only.

Annotations

@Override