11.3. The Multi-Source Column

When a model is marked as multi-source, the engine will add or use an existing column on each table to represent the source name values. In the above vdb.xml the column would return chicago , la , newyork for each of the respective sources. The name of the column defaults to SOURCE_NAME, but is configurable by setting the model property multisource.columnName . If a column already exists on the table (or an IN procedure parameter) with the same name, the engine will assume that it should represent the multi-source column and it will not be used to retrieve physical data. If the multi-source column is not present, the generated column will be treated as a pseudo column which is not selectable via wildcards (* nor tbl.*).

This allows queries like the following:

select * from table where SOURCE_NAME = 'newyork'
update table column=value where SOURCE_NAME='chicago'
delete from table where column = x and SOURCE_NAME='la'
insert into table (column, SOURCE_NAME) VALUES ('value', 'newyork')

select * from table where SOURCE_NAME = 'newyork'
update table column=value where SOURCE_NAME='chicago'
delete from table where column = x and SOURCE_NAME='la'
insert into table (column, SOURCE_NAME) VALUES ('value', 'newyork')