Package org.apache.drill.exec.ops

Class ViewExpansionContext

java.lang.Object
org.apache.drill.exec.ops.ViewExpansionContext
public class ViewExpansionContext extends Object
Contains context information about view expansion(s) in a query. Part of .QueryContext. Before expanding a view into its definition, as part of the DrillViewTable.toRel(org.apache.calcite.plan.RelOptTable.ToRelContext, org.apache.calcite.plan.RelOptTable), first a ViewExpansionContext.ViewExpansionToken is requested from ViewExpansionContext through reserveViewExpansionToken(String). Once view expansion is complete, a token is released through ViewExpansionContext.ViewExpansionToken.release(). A view definition itself may contain zero or more views for expanding those nested views also a token is obtained. Ex: Following are the available view tables: { "view_1", "view_2", "view_3", "view_4" }. Corresponding owners are {"view1Owner", "view2Owner", "view3Owner", "view4Owner"}. Definition of "view4" : "SELECT field4 FROM view3" Definition of "view3" : "SELECT field4, field3 FROM view2" Definition of "view2" : "SELECT field4, field3, field2 FROM view1" Definition of "view1" : "SELECT field4, field3, field2, field1 FROM someTable" Query is: "SELECT * FROM view4". Steps: 1. "view4" comes for expanding it into its definition 2. A token "view4Token" is requested through reserveViewExpansionToken(String view4Owner) 3. "view4" is called for expansion. As part of it 3.1 "view3" comes for expansion 3.2 A token "view3Token" is requested through reserveViewExpansionToken(String view3Owner) 3.3 "view3" is called for expansion. As part of it 3.3.1 "view2" comes for expansion 3.3.2 A token "view2Token" is requested through reserveViewExpansionToken(String view2Owner) 3.3.3 "view2" is called for expansion. As part of it 3.3.3.1 "view1" comes for expansion 3.3.3.2 A token "view1Token" is requested through reserveViewExpansionToken(String view1Owner) 3.3.3.3 "view1" is called for expansion 3.3.3.4 "view1" expansion is complete 3.3.3.5 Token "view1Token" is released 3.3.4 "view2" expansion is complete 3.3.5 Token "view2Token" is released 3.4 "view3" expansion is complete 3.5 Token "view3Token" is released 4. "view4" expansion is complete 5. Token "view4Token" is released.