attempted to return null from a method with a primitive return type (int).

cause of the error¶

The reason for this error is that the sql statement did not query the data, and the return was `null`. And the dao layer method we defined returns as int, and the following prompt will appear:

return null from a method with a primitive return type (int). (Trying to return null from a method with a primitive return type (int))

Ingeter is a wrapper class of int, the initial value of int is 0, and the initial value of Ingeter is null.

solution¶

Change the return type of the dao layer to Integer.