Solving the “The given value of type String from the data source cannot be converted to type nvarchar of the specified target column” issue

If you’ve ever encountered the error message “The given value of type String from the data source cannot be converted to type nvarchar of the specified target column.” when working with a database, you know how frustrating it can be to debug. This error message typically occurs when there is a data type mismatch between the source data and the target column in a database. In this article, we’ll show you how to solve this issue when you don’t know which property in the source data is causing the problem.

One way to identify which property is causing the problem is to check the maximum length of each string property in the source data and compare it to the maximum length of the corresponding column in the target database table. Here’s some C# code that can help you do this:

var maxLengths = new Dictionary<string, int>();
foreach (var column in columns)
{
    var properties = column.GetType().GetProperties();
    foreach (var prop in properties)
    {
        if (prop.GetValue(column) is string value)
        {
            int length = value.Length;
            if (maxLengths.ContainsKey(prop.Name))
            {
                maxLengths[prop.Name] = Math.Max(maxLengths[prop.Name], length);
            }
            else
            {
                maxLengths.Add(prop.Name, length);
            }
        }
    }
}

foreach (var kvp1 in maxLengths)
{
    Console.WriteLine($"Max length of {kvp1.Key}: {kvp1.Value}");
}

To solve this issue, you may need to either truncate the string value to fit within the maximum length of the column or modify the column in the database to allow for a larger maximum length.