A boolean variable with a null value

C # Language Reference Bool (C # reference)

The bool keyword is the alias of system...:. boolean. It is used to declare variables to store Boolean values true and false.

If you need a Boolean variable with a null value, use bool ?. For more information, see the empty type (C # programming guide ).

The following code is used to understand how to read data from the database. 1. Read the public static object setvalue (bool? Inputvalue) {OBJ outvalue = dbnull. value; // because in the dB, the null value has one specifical. If (inputvalue! = NULL) {outvalue = (object) inputvalue;} return outvalue;} 2. Read from the database.

Public static bool? Getboolandnullfield (Object inputvalue)
{

Bool? Outvalue = false;

If (inputvalue = NULL)

{

Outvalue = (bool ?) NULL;

}

Else if (inputvalue = dB. value)

{

Outvalue = (bool ?) NULL;

}

Else

Outvalue = (bool ?) Inputvalue;

Return outvalue;
}

The above two functions are encapsulated.

The following is an example:

We just read the database, such as parm. Add (New dbparameter ("@ paraname1", dbtype. Boolean, setvalue (input )));

In this way, we will convert it to the corresponding Boolean to read into the database. As for null, it is because the database has a special null value. if it is null, the database reads null.

 

The same is true for database reading.

Getboolandnullfield (R ["columnname1"]);

In this example, we can encapsulate such types as string, Int, datetime, short, and decimal to read null correctly in the database.