How to Handle DBNull Values When Assigning to SQL Parameters in C#?

Cannot assign DBNull value to SqlParameter

When trying to assign a null value to SqlParameter, the following code will report an error:

<code class="language-csharp">SqlParameter[] parameters = new SqlParameter[1];    
SqlParameter planIndexParameter = new SqlParameter("@AgeIndex", SqlDbType.Int);
planIndexParameter.Value = (AgeItem.AgeIndex == null) ? DBNull.Value : AgeItem.AgeIndex;
parameters[0] = planIndexParameter;</code>

The problem is that the ?: operator cannot determine the return type because it may be an int type value or a DBNull type value, and the two are incompatible.

Solution:

To solve this problem, you can choose the following methods:

• Casting: Casts the AgeIndex instance to type object, which satisfies the requirements of the ?: operator:

<code class="language-csharp">SqlParameter[] parameters = new SqlParameter[1];     
SqlParameter planIndexParameter = new SqlParameter("@AgeIndex", SqlDbType.Int);
planIndexParameter.Value = (object)AgeItem.AgeIndex ?? DBNull.Value;
parameters[0] = planIndexParameter; </code>

• Use the null coalescing operator: Use the ?? null coalescing operator:

<code class="language-csharp">SqlParameter[] parameters = new SqlParameter[1];     
SqlParameter planIndexParameter = new SqlParameter("@AgeIndex", SqlDbType.Int);
planIndexParameter.Value = AgeItem.AgeIndex ?? DBNull.Value;
parameters[0] = planIndexParameter; </code>

According to the MSDN documentation for the ?: operator, first_expression and second_expression must be of the same type, or one type can be implicitly converted to the other.

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