Do you want to add some columns from another table?
Or maybe do you want to put in some selections by default?
Implement ExtendedExtity interface.
How to add another table column
If you want to add another columns to the entity, first implement their interfaces.
Next, to put them into joinedColumns() method in the same way as they are into Entity method columns().
Finally, join table containing columns into enhanceQuery() method. You should join tables related.
Limit selection by adding where clause
To limit selection, just put your where clause into enchaneQuery() method.