How to Handle Null Values in LINQ Sum() to Avoid 'The Cast to Value Type 'Int32' Failed' Error?

Null handling in LINQ queries: Resolving "Cannot convert to value type 'Int32'" error

This code uses a LINQ query to retrieve the total credit history amount for a specific user ID. When there are no records in the CreditHistory table, you will encounter errors due to returning null values.

Rewrite query to handle null values

The error occurs because the Sum() method expects a non-null value, but the query may return a null value. To solve this problem, you can modify the query to accept nullable types using the ?? operator or the DefaultIfEmpty() method.

Use the ?? operator

The

?? operator can be used to handle null values ​​by specifying a default value:

<code class="language-csharp">var creditsSum = (from u in context.User
                  join ch in context.CreditHistory on u.ID equals ch.UserID
                  where u.ID == userID
                  select (int?)ch.Amount).Sum() ?? 0;</code>

This code first converts the Amount property to an int? to indicate that it can be null. The sum is then calculated using the Sum() method, which returns an int?. Then use the ?? operator to assign a default value of 0 if the result is empty.

Use the DefaultIfEmpty() method

Alternatively, you can use the DefaultIfEmpty() method to handle empty values:

<code class="language-csharp">var creditsSum = (from u in context.User
                  join ch in context.CreditHistory on u.ID equals ch.UserID
                  where u.ID == userID
                  select ch.Amount).DefaultIfEmpty(0).Sum();</code>

This method adds a default value (0) to the sequence before performing the Sum() operation. If the sequence contains no elements, the default value will be used for sum calculations.

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