Returning DataTables in WCF/.NET: A Comprehensive Guide

Returning a DataTable from a WCF (.NET) service can often be a challenging task, as it frequently raises significant questions and debates among developers about best practices. Whether you’re developing a fresh application or trying to optimize existing services, understanding how to manage the serialization of DataTable is essential. This blog post dives into the common issues developers face when returning DataTables and provides effective solutions to overcome them.

The Problem: CommunicationException when querying a database

Many developers encounter a problem when they attempt to populate a DataTable by directly querying a database. They might receive a CommunicationException message stating:

“The underlying connection was closed: The connection was closed unexpectedly.”

This error may be perplexing, especially when creating and returning a test DataTable from scratch works flawlessly. Why does the database population complicate things? Let’s explore the solution and uncover the reasons behind this behavior.

Understanding the Solution

After conducting thorough research and tests, including utilizing tools like the SvcTraceViewer utility, the following solutions have proven effective for solving this problem:

1. Configure Max..Size Properties

When encountering serialization issues with DataTables, it often helps to adjust the Max..Size properties in your configuration file. The reason this is necessary hinges on WCF’s limitations on message sizes. Follow these tips:

• Increase the maxArrayLength and maxStringContentLength settings within your web.config or app.config under the <binding> section.

Example:

<binding name="BasicHttpBinding_IService" maxArrayLength="2147483647" maxStringContentLength="2147483647">

• Regularly check for updates to your Service Reference; changes made on the server side must also be reflected on the client side. If you’re facing issues, manually adjust these settings on both ends.

2. Ensure DataTable is Serializable

An essential requirement for successfully returning a DataTable is that it needs to have a name to ensure serialization. The default constructor creates a DataTable without a name, making it non-serializable. Here’s how you can remedy this:

• When creating a new DataTable, make sure to provide it with a name explicitly.

return new DataTable("SomeName"); // Properly named DataTable

Alternatively, you can assign a name after creating the table:

var table = new DataTable();
table.TableName = "SomeName"; // Assign a name later

3. Creating a Named DataTable from the Database

Before hitting the database to populate the DataTable, make sure that the DataTable has been properly initialized and named. Given that a named DataTable is essential for serialization, apply this during the data retrieval process. Here’s a simplified approach to fetching the data:

[DataContract]
public DataTable GetTbl()
{
    DataTable tbl = new DataTable("testTbl"); // Ensure table has a name
    // Call your SQL retrieval method to fill tbl
    return tbl;
}

Conclusion

By following these established practices, you can successfully return a DataTable from your WCF/.NET service without encountering unexpected communication errors. Remember that properly naming your DataTables and adjusting size properties are crucial elements in the troubleshooting process.

Hopefully, this guide helps clarify some of the challenges related to returning a DataTable in WCF, equipping you with the knowledge to implement effective solutions in your projects. Happy coding!