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How to Handle Null Values in LINQ Sum() to Avoid 'The Cast to Value Type 'Int32' Failed' Error?
How to Handle Null Values in LINQ Sum() to Avoid 'The Cast to Value Type 'Int32' Failed' Error?
Jan 10, 2025 pm 08:52 PM
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:
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;
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:
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();
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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