It is not bad idea if you want to use it over classic SQL data access, ou may face performance issues. Personally using core is preferred choice.There are performance problems reported earlier and Microsoft has some improvements in EF6 than 4. Solutions - Generally you can split into multiple EDMX files and work for large DB.Please refer article here for performance problems -https://blogs.msdn.microsoft.com/adonet/2008/11/24/working-with-large-models-in-entity-framework-part-1/ https://blogs.msdn.microsoft.com/adonet/2008/11/25/working-with-large-models-in-entity-framework-part-2/

For. Should we use entity framework with large databases which has 300 or 400 or more tables? Is there a performance overhead? If yes, how should we design our edmx?If no, then what is the best way?I dont know why but i always stick with core functionalities actually entity framework is built from core right, so use core.

No. Use core DB functionalities

Should we use entity framework with large databases which has 300 or 400 or more tables? Is there a performance overhead? If yes, how should we design our edmx?If no, then what is the best way?