Execute the insert statement, object val = cmd. ExecuteScalar () val = null, jqueryvalnull

Execute the insert statement, object val = cmd. ExecuteScalar () val = null, jqueryvalnull

An error occurred while writing the interface: The empty object cannot be converted to the value type.

Because we use petapoco, after debugging, we found that

Object val = cmd. ExecuteScalar () error. val = null

Because I am executing an insert statement, and the function of this method is to return only the first column of the first row of the dataset.

Solution:

① The simplest one

Call the db. Execute method on the service layer instead of the ExecuteScalar method.

② Add an SQL code in SQL, select 1. Because ExecuteScalar is the first column in the first row of the returned Dataset