


How to Avoid 'Unable to cast object of type 'System.DBNull' to type 'System.String'' Errors in C# Database Queries?
Jan 25, 2025 am 10:16 AMAddressing the "Unable to cast object of type 'System.DBNull' to type 'System.String'" Error in Database Queries
Database interactions can sometimes throw the "Unable to cast object of type 'System.DBNull' to type 'System.String'" exception. This happens when trying to directly convert a System.DBNull
database value into a string. Let's explore solutions to prevent this.
Here's a revised code snippet demonstrating a robust approach:
public string GetCustomerNumber(Guid id) { object accountNumber = DBSqlHelperFactory.ExecuteScalar(connectionStringSplendidCRM, CommandType.StoredProcedure, "spx_GetCustomerNumber", new SqlParameter("@id", id)); return accountNumber is DBNull ? string.Empty : accountNumber.ToString(); }
This improved version avoids direct casting. It uses the conditional operator (?:
) to check if accountNumber
is DBNull
. If it is, an empty string is returned; otherwise, ToString()
safely converts the object to a string.
For a more versatile solution, consider this generic function:
public static T ConvertFromDBVal<T>(object obj) { if (obj == null || obj == DBNull.Value) { return default(T); // Returns the default value for the specified type } return (T)obj; }
This generic function handles various data types. You specify the target type using type parameters, allowing for safe and type-correct conversions:
return ConvertFromDBVal<string>(accountNumber);
This approach is cleaner, more reusable, and less prone to casting errors. By implementing these methods, you can effectively handle DBNull
values and prevent the "Unable to cast object of type 'System.DBNull' to type 'System.String'" error from disrupting your database operations.
The above is the detailed content of How to Avoid 'Unable to cast object of type 'System.DBNull' to type 'System.String'' Errors in C# Database Queries?. For more information, please follow other related articles on the PHP Chinese website!

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