Package org.eclipse.persistence.internal.expressions

Class DataExpression

    • Constructor Detail

      • DataExpression

        public DataExpression()
        DataExpression constructor comment.

    • 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.
        Overrides:
        equals in class Expression

      • addDerivedField

        public void addDerivedField​(Expression addThis)

      • addDerivedTable

        public void addDerivedTable​(Expression addThis)

      • 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)

      • assignAlias

        protected void assignAlias​(DatabaseTable alias,
                           DatabaseTable table)
        INTERNAL: Alias a particular table within this node

      • clearAliases

        public void clearAliases()
        INTERNAL:

      • getAliasedField

        public DatabaseField getAliasedField()
        INTERNAL: Return the field appropriately aliased

      • getField

        public Expression getField​(String fieldName)
        Description copied from class: Expression
        ADVANCED: Return an expression representing a field in a data-level query. This is used internally in EclipseLink, or to construct queries involving fields and/or tables that are not mapped.

        Example: 

          builder.getField("ADDR_ID").greaterThan(100);
  builder.getTable("PROJ_EMP").getField("TYPE").equal("S");
        Overrides:
        getField in class Expression

      • getField

        public Expression getField​(DatabaseField field)
        Description copied from class: Expression
        ADVANCED: Return an expression representing a field in a data-level query. This is used internally in EclipseLink, or to construct queries involving fields and/or tables that are not mapped.

        Example: 

          builder.getField(aField).greaterThan(100);
        Overrides:
        getField in class Expression

      • getContainingDescriptor

        public ClassDescriptor getContainingDescriptor()
        INTERNAL: Return the descriptor which contains this query key.

      • getQueryKeyOrNull

        public QueryKey getQueryKeyOrNull()

      • getTable

        public Expression getTable​(String tableName)
        Description copied from class: Expression
        ADVANCED: Return an expression representing a table in a data-level query. This is used internally in EclipseLink, or to construct queries involving fields and/or tables that are not mapped.

        Example: 

          builder.getTable("PROJ_EMP").getField("TYPE").equal("S");
        Overrides:
        getTable in class Expression

      • getTable

        public Expression getTable​(DatabaseTable table)
        Description copied from class: Expression
        ADVANCED: Return an expression representing a table in a data-level query. This is used internally in EclipseLink, or to construct queries involving fields and/or tables that are not mapped.

        Example: 

          builder.getTable(linkTable).getField("TYPE").equal("S");
        Overrides:
        getTable in class Expression

      • getTableAliases

        public TableAliasLookup getTableAliases()
        INTERNAL: Return the aliases used. For CR#2456 must never lazily initialize as also used for Expression identity.
        Overrides:
        getTableAliases in class Expression

      • hasBeenNormalized

        public boolean hasBeenNormalized()
        INTERNAL: Did the normalizer already add additional joins to the where clause due to this query key representing a foreign reference mapping? This insures that join criteria (for any query key expression) is not added twice.

        New meaning: DataExpressions are often iterated on multiple times during normalize, but Function/Relation expressions only once. Adding a has been normalized flag improves performance and is required in some applications, such as have temporal query criteria been added.

      • hasBeenAliased

        public boolean hasBeenAliased()
        Description copied from class: Expression
        INTERNAL: Answers if the database tables associated with this expression have been aliased. This insures the same tables are not aliased twice.
        Overrides:
        hasBeenAliased in class Expression

      • hasDerivedFields

        protected boolean hasDerivedFields()

      • hasDerivedTables

        protected boolean hasDerivedTables()

      • isAttribute

        public boolean isAttribute()
        INTERNAL:

      • getAlias

        public Expression getAlias​(Expression subSelect)
        ADVANCED: Return an expression representing a sub-select in the from clause.

        Example: 

          builder.getAlias(builder.subQuery(reportQuery)).get("type").equal("S");
        Overrides:
        getAlias in class Expression

      • postCopyIn

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

      • setHasBeenNormalized

        public void setHasBeenNormalized​(boolean value)

      • setTableAliases

        public void setTableAliases​(TableAliasLookup tableAliases)
        INTERNAL: For CR#2456, Table identity involves having two tables sharing the same aliasing table.

      • tableAliasesDescription

        public String tableAliasesDescription()