How to Solve the 'Object cannot be cast from DBNull to other types' Error in C#?

Fix "Object cannot be converted from DBNull to other type" error

This error usually occurs when trying to convert a DBNull value to another data type. In your specific case, the problem may occur at the following line of code in the Create() method:

<code>DataTO.Id = Convert.ToInt64(dataAccCom.GetParameterValue(IDbCmd, "op_Id"));</code>

This conversion will fail if the output parameter "op_Id" returns a DBNull value. To resolve this issue, you should check the DBNull value and handle it appropriately. The following is the modified code version:

<code>var outputParam = dataAccCom.GetParameterValue(IDbCmd, "op_Id");
if (outputParam is DBNull)
    DataTO.Id = 0; // 或根据需要分配默认值
else
    DataTO.Id = Convert.ToInt64(outputParam);</code>

By adding this check, you ensure that the conversion is only performed if the output parameter contains a valid value. This should eliminate the "Object cannot be converted from DBNull to another type" error.

Note that this error can also occur if any other parameter is set to DBNull and a cast is attempted on that parameter. Please review your code carefully to identify any potential instances of this problem.

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