How to insert null value in Database through param

问题:

I have a datetime datatype : dttm

Also the database field type is datatime

Now I am doing this:

if (dttm.HasValue)
{
    cmd.Parameters.AddWithValue("@dtb", dttm);
}
else
{
    // It should insert null value into database
    // through cmd.Parameters.AddWithValue("@dtb", _____)
}

How can this be done.

回答1:

Use DBNull.Value

if (dttm.HasValue)
{
    cmd.Parameters.AddWithValue("@dtb", dttm);
}
else
{
    cmd.Parameters.AddWithValue("@dtb", DBNull.Value)
}

回答2:

This can be done using the null-coalescing operator: if the value of dttm is null the DBNull.Value will be inserted otherwise the value of dttm will be used

cmd.Parameters.AddWithValue("@dtb", dttm ?? (object) DBNull.Value);

This will eliminate the need for the if statment

回答3:

if your field allows null value;

if (dttm.HasValue)
{
    cmd.Parameters.AddWithValue("@dtb", dttm);
}
else
{
    cmd.Parameters.AddWithValue("@dtb", DBNull.Value)
}