How to Handle the 'Object cannot be cast from DBNull to other types' Exception in C#?

Troubleshooting the "Object cannot be cast from DBNull to other types" Exception in C#

This common C# error occurs when your code attempts to convert a database null value into a non-nullable data type. Here's a breakdown of how to fix it:

1. Stored Procedure Null Handling:

Your database stored procedures must explicitly manage null values. Use SQL's null-coalescing operator (ISNULL or COALESCE) or CASE statements to provide default values for nullable columns.

2. C# Parameter Type Matching:

When defining parameters for your IDbCommand object, ensure the C# data types precisely match the database column types. Crucially, correctly handle nullable database fields using nullable types in C# (e.g., long? instead of long).

3. Safe Casting of Output Parameters:

The error often stems from casting output parameters. Instead of directly casting, always check for DBNull before converting:

var outputParam = dataAccCom.GetParameterValue(IDbCmd, "op_Id");
DataTO.Id = outputParam is DBNull ? 0 : Convert.ToInt64(outputParam); // Or a more appropriate default

This code uses the conditional operator to assign a default value (0 in this example) if outputParam is DBNull. Choose a default value that makes sense in your application's context.

4. Robust ReplaceNull Methods:

Review your ReplaceNull methods (if used). They must handle null values for all data types appropriately. Return a suitable default (e.g., 0 for numbers, "" for strings) for nullable fields in your DataTO object.

By implementing these checks and using appropriate default values, you'll prevent the "Object cannot be cast from DBNull to other types" exception and create more robust code.

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