Module org.eclipse.persistence.core
Package org.eclipse.persistence.internal.expressions

Class CompoundExpression

java.lang.Object
org.eclipse.persistence.expressions.Expression
org.eclipse.persistence.internal.expressions.CompoundExpression
All Implemented Interfaces:
Serializable, Cloneable
Direct Known Subclasses:
LogicalExpression, RelationExpression
public abstract class CompoundExpression extends Expression
Abstract class for expression that have exactly two children, such as and/or and relations.
See Also:

  • Field Details

  • Constructor Details

    • CompoundExpression

      protected CompoundExpression()

  • Method Details

    • 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.
      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

    • aliasForTable

      public DatabaseTable aliasForTable(DatabaseTable table)
      INTERNAL: Find the alias for a given table from the first or second child in the additionalOuterJoinCriteria
      Overrides:
      aliasForTable in class Expression

    • 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:

    • create

      public Expression create(Expression base, Object singleArgument, ExpressionOperator operator)
      INTERNAL:
      Overrides:
      create in class Expression

    • create

      public Expression create(Expression base, List arguments, ExpressionOperator operator)
      INTERNAL:
      Overrides:
      create in class Expression

    • descriptionOfNodeType

      public String descriptionOfNodeType()
      INTERNAL: Used for debug printing.
      Overrides:
      descriptionOfNodeType in class Expression

    • getBuilder

      public ExpressionBuilder 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)
      Specified by:
      getBuilder in class Expression

    • getFirstChild

      public Expression getFirstChild()

    • getOperator

      public ExpressionOperator getOperator()
      Description copied from class: Expression
      INTERNAL: Most expression have operators, so this is just a convenience method.
      Overrides:
      getOperator in class Expression

    • getPlatformOperator

      public ExpressionOperator getPlatformOperator(DatabasePlatform platform)

    • getSecondChild

      public Expression getSecondChild()

    • initializePlatformOperator

      public void initializePlatformOperator(DatabasePlatform platform)
      INTERNAL:

    • isCompoundExpression

      public boolean isCompoundExpression()
      Description copied from class: Expression
      INTERNAL:
      Overrides:
      isCompoundExpression in class Expression

    • iterateOn

      public void iterateOn(ExpressionIterator iterator)
      INTERNAL: For iterating using an inner class
      Overrides:
      iterateOn in class Expression

    • normalize

      public Expression normalize(ExpressionNormalizer normalizer)
      INTERNAL: Normalize into a structure that is printable. Also compute printing information such as outer joins.
      Overrides:
      normalize in class Expression

    • validateNode

      public void validateNode()
      Do any required validation for this node. Throw an exception if it's incorrect. Ensure that both sides are not data expressions.
      Overrides:
      validateNode in class Expression

    • postCopyIn

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

    • printSQL

      public void printSQL(ExpressionSQLPrinter printer)
      INTERNAL: Print SQL
      Specified by:
      printSQL in class Expression

    • printJava

      public void printJava(ExpressionJavaPrinter printer)
      INTERNAL: Print java for project class generation
      Overrides:
      printJava in class Expression

    • rebuildOn

      public Expression rebuildOn(Expression newBase)
      INTERNAL: This expression is built on a different base than the one we want. Rebuild it and return the root of the new tree
      Specified by:
      rebuildOn in class Expression
      See Also:

    • 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.
      Specified by:
      resetPlaceHolderBuilder in class Expression

    • setFirstChild

      protected void setFirstChild(Expression firstChild)

    • setOperator

      public void setOperator(ExpressionOperator newOperator)

    • setSecondChild

      protected void setSecondChild(Expression secondChild)

    • twistedForBaseAndContext

      public Expression twistedForBaseAndContext(Expression newBase, Expression context, Expression oldBase)
      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.
      Overrides:
      twistedForBaseAndContext in class Expression

    • writeDescriptionOn

      public void writeDescriptionOn(BufferedWriter writer) throws IOException
      INTERNAL: Used to print a debug form of the expression tree.
      Overrides:
      writeDescriptionOn in class Expression
      Throws:
      IOException

    • writeSubexpressionsTo

      public void writeSubexpressionsTo(BufferedWriter writer, int indent) throws IOException
      INTERNAL: Used for toString for debugging only.
      Overrides:
      writeSubexpressionsTo in class Expression
      Throws:
      IOException

    • shallowClone

      public Expression shallowClone()
      INTERNAL: Clear the builder when cloning.
      Overrides:
      shallowClone in class Expression