Coding⏱️ 2 min read📅 2026-05-31

How to Fix: The cast to value type 'Int32' failed because the materialized value is null

Error when joining tables with null values and summing a nullable field.

Quick Answer: Use the nullable type or include a default value in the select clause to avoid the error.

📋 Table of Contents

  1. 🚀 How to Resolve This Issue
  2. 💡 Conclusion

The error occurs because the `Sum()` method is trying to calculate the sum of a collection that contains null values. When there are no records in the `CreditHistory` table, the materialized value (i.e., the amount) becomes null. To resolve this issue, you can modify the query to use the `DefaultIfEmpty()` method to replace null values with a default value.

🚀 How to Resolve This Issue

Method 1: Using DefaultIfEmpty()

  1. Step 1: Replace the `Sum()` method with `DefaultIfEmpty(0)` to replace null values with a default value of 0.

Example Code:

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();

💡 Conclusion

By using `DefaultIfEmpty()`, you can avoid the error and get a meaningful sum of credits even when there are no records in the `CreditHistory` table.

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