Скачать или смотреть Fixing Null Return from builder.Configuration.GetConnectionString("DefaultConnection") in ASP.NET C

Learn why GetConnectionString("DefaultConnection") returns null in ASP.NET Core and how to correctly structure your appsettings.json to fix it.
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This video is based on the question https://stackoverflow.com/q/79471477/ asked by the user 'CoderForHire' ( https://stackoverflow.com/u/793497/ ) and on the answer https://stackoverflow.com/a/79471614/ provided by the user 'marc_s' ( https://stackoverflow.com/u/13302/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding the Problem

In an ASP.NET Core 6 Web API project, it's common to retrieve database connection strings via

[[See Video to Reveal this Text or Code Snippet]]

However, sometimes this call returns null even though you've defined the connection string in your appsettings.json files.

Typical Scenario

You might have your connection string defined under a custom section like Data:

[[See Video to Reveal this Text or Code Snippet]]

But calling .GetConnectionString("DefaultConnection") returns null.

Why Does This Happen?

GetConnectionString() is a convenience method that looks specifically for a top-level JSON section called ConnectionStrings. It does not search deeper nested sections like Data.

Therefore, if your connection strings are not under ConnectionStrings, the call will return null.

Correct Structure for Connection Strings

Your appsettings.json should have the following structure:

[[See Video to Reveal this Text or Code Snippet]]

Key Points:

Place ConnectionStrings at the root level.

The connection string value is a string, not an object. No nesting inside DefaultConnection.

Summary Steps to Fix

Open your appsettings.json and appsettings.Development.json.

Move (or copy) the connection string entry into a top-level ConnectionStrings section.

Make sure the structure is:

[[See Video to Reveal this Text or Code Snippet]]

Remove or adjust any conflicting nested Data sections if necessary.

Additional Tips

Restart the application after making changes to config files.

Use builder.Configuration.GetSection("ConnectionStrings") to debug and check values.

Consider using strongly typed configuration with options pattern for easier management.

By aligning your configuration format with what GetConnectionString() expects, your application will correctly retrieve the connection string and connect to your database without returning null.