Explain the purpose of the .csproj file in an ASP.NET application

The .csproj file tells dotnet how to build the ASP.NET application. It’s one of the most important files in an ASP.NET project.

An ASP.NET project can depend on third-party libraries developed by other developers. Usually, these libraries are installed as Nuget packages using Nuget package manager. Once you install a package using Nuget, the name of the package along with its version is listed in the .csproj file.

If you are familiar with Node.js, you can think of a .csproj file as a package.json file. Upon running the ‘dotnet restore’ command, dotnet uses the .csproj file to determine the packages to install from Nuget.

To compile an ASP.NET application, the compiler needs information such as the version of the dotnet framework, the type of the application, etc. A .csproj file stores all this information that allows dotnet to build and compile the project.

Consider the following example of a .csproj file that contains the various Nuget packages that an ASP.NET application depends on, along with other information dotnet tooling needs to build the application.

<?xml version="1.0" encoding="UTF-8"?>
<Project Sdk="Microsoft.NET.Sdk.Web">
   <PropertyGroup>
      <TargetFramework>net5.0</TargetFramework>
   </PropertyGroup>
   <ItemGroup>
      <PackageReference Include="SQLite" Version="3.13.0" />
      <PackageReference Include="Microsoft.Data.Sqlite.Core" Version="6.0.0-preview.4.21253.1" />
      <PackageReference Include="Microsoft.Extensions.Primitives" Version="6.0.0-preview.4.21253.7" />
      <PackageReference Include="Newtonsoft.Json" Version="13.0.1" />
      <PackageReference Include="log4net" Version="2.0.12" />
   </ItemGroup>
</Project>

In this example, the file tells dotnet that it’s a web application that depends on .NET 5 framework. It also lists various dependencies such as SQLite and logfornet that the application depends upon.

Here are some of the benefits of the .csproj file in ASP.NET Core vs. the older versions of ASP.NET:

• Automatic file included: In older versions of ASP.NET, the .csproj file contained a listing for every file in the project. Now, the files are automatically included.

• No GUIDs: Earlier, the .csproj file contained many GUIDs. Now they are rarely used.

• No DLL paths: In older versions, you had to include the path to the Nuget .DLL files that your project depended on. The new version allows you to directly refer to the Nuget packages without having to specify the path on the disk.