Package references (PackageReference) in project files

Package references, using the PackageReference node, manage NuGet dependencies directly within project files (as opposed to a separate packages.config file). Using PackageReference, as it's called, doesn't affect other aspects of NuGet; for example, settings in NuGet.config files (including package sources) are still applied as explained in Configuring NuGet Behavior.

With PackageReference, you can also use MSBuild conditions to choose package references per target framework, configuration, platform, or other groupings. It also allows for fine-grained control over dependencies and content flow. (See For more details NuGet pack and restore as MSBuild targets.)

By default, PackageReference is used for .NET Core projects, .NET Standard projects, and UWP projects targeting Windows 10 Build 15063 (Creators Update) and later, with the exception of C++ UWP projects. .NET Framework projects support PackageReference, but currently default to packages.config. To use PackageReference, migrate the dependencies from packages.config into your project file, then remove packages.config.

Adding a PackageReference

Add a dependency in your project file using the following syntax:

<ItemGroup>
    <!-- ... -->
    <PackageReference Include="Contoso.Utility.UsefulStuff" Version="3.6.0" />
    <!-- ... -->
</ItemGroup>

Controlling dependency version

The convention for specifying the version of a package is the same as when using packages.config:

<ItemGroup>
    <!-- ... -->
    <PackageReference Include="Contoso.Utility.UsefulStuff" Version="3.6.0" />
    <!-- ... -->
</ItemGroup>

In the example above, 3.6.0 means any version that is >=3.6.0 with preference for the lowest version, as described on Package versioning.

Using PackageReference for a project with no PackageReferences

Advanced: If you have no packages installed in a project (no PackageReferences in project file and no packages.config file), but want the project to be restored as PackageReference style, you can set a Project property RestoreProjectStyle to PackageReference in your project file.

<PropertyGroup>
    <!--- ... -->
    <RestoreProjectStyle>PackageReference</RestoreProjectStyle>
    <!--- ... -->
</PropertyGroup>    

This may be useful, if you reference projects which are PackageReference styled (existing csproj or SDK-style projects). This will enable packages that those projects refer to, to be "transitively" referenced by your project.

Floating Versions

Floating versions are supported with PackageReference:

<ItemGroup>
    <!-- ... -->
    <PackageReference Include="Contoso.Utility.UsefulStuff" Version="3.6.*" />
    <PackageReference Include="Contoso.Utility.UsefulStuff" Version="3.6.0-beta*" />
    <!-- ... -->
</ItemGroup>

Controlling dependency assets

You might be using a dependency purely as a development harness and might not want to expose that to projects that will consume your package. In this scenario, you can use the PrivateAssets metadata to control this behavior.

<ItemGroup>
    <!-- ... -->

    <PackageReference Include="Contoso.Utility.UsefulStuff" Version="3.6.0">
        <PrivateAssets>all</PrivateAssets>
    </PackageReference>

    <!-- ... -->
</ItemGroup>

The following metadata tags control dependency assets:

Tag Description Default Value
IncludeAssets These assets will be consumed all
ExcludeAssets These assets will not be consumed none
PrivateAssets These assets will be consumed but won't flow to the parent project contentfiles;analyzers;build

Allowable values for these tags are as follows, with multiple values separated by a semicolon except with all and none which must appear by themselves:

Value Description
compile Contents of the lib folder and controls whether your project can compile against the assemblies within the folder
runtime Contents of the lib and runtimes folder and controls whether these assemblies will be copied out to the build output directory
contentFiles Contents of the contentfiles folder
build Props and targets in the build folder
analyzers .NET analyzers
native Contents of the native folder
none None of the above are used.
all All of the above (except none)

In the following example, everything except the content files from the package would be consumed by the project and everything except content files and analyzers would flow to the parent project.

<ItemGroup>
    <!-- ... -->

    <PackageReference Include="Contoso.Utility.UsefulStuff" Version="3.6.0">
        <IncludeAssets>all</IncludeAssets>
        <ExcludeAssets>contentFiles</ExcludeAssets>
        <PrivateAssets>contentFiles;analyzers</PrivateAssets>
    </PackageReference>

    <!-- ... -->
</ItemGroup>

Note that because build is not included with PrivateAssets, targets and props will flow to the parent project. Consider, for example, that the reference above is used in a project that builds a NuGet package called AppLogger. AppLogger can consume the targets and props from Contoso.Utility.UsefulStuff, as can projects that consume AppLogger.

Adding a PackageReference condition

You can use a condition to control whether a package is included, where conditions can use any MSBuild variable or a variable defined in the targets or props file. However, at presently, only the TargetFramework variable is supported.

For example, say you're targeting netstandard1.4 as well as net452 but have a dependency that is applicable only for net452. In this case you don't want a netstandard1.4 project that's consuming your package to add that unnecessary dependency. To prevent this, you specify a condition on the PackageReference as follows:

<ItemGroup>
    <!-- ... -->
    <PackageReference Include="Newtonsoft.Json" Version="9.0.1" Condition="'$(TargetFramework)' == 'net452'" />
    <!-- ... -->
</ItemGroup>

A package built using this project will show that Newtonsoft.Json is included as a dependency only for a net452 target:

The result of applying a Condition on PackageReference with VS2017

Conditions can also be applied at the ItemGroup level and will apply to all children PackageReference elements:

<ItemGroup Condition = "'$(TargetFramework)' == 'net452'">
    <!-- ... -->
    <PackageReference Include="Newtonsoft.Json" Version="9.0.1" />
    <PackageReference Include="Contoso.Utility.UsefulStuff" Version="3.6.0" />
    <!-- ... -->
</ItemGroup>

Locking dependencies

This feature is available with NuGet 4.9 or above and with Visual Studio 2017 15.9 or above.

Input to NuGet restore is a set of Package References from the project file (top-level or direct dependencies) and the output is a full closure of all the package dependencies including transitive dependencies. NuGet tries to always produce the same full closure of package dependencies if the input PackageReference list has not changed. However, there are some scenarios where it is unable to do so. For example:

  • When you use floating versions like <PackageReference Include="My.Sample.Lib" Version="4.*"/>. While the intention here is to float to the latest version on every restore of packages, there are scenarios where users require the graph to be locked to a certain latest version and float to a later version, if available, upon an explicit gesture.

  • A newer version of the package matching PackageReference version requirements is published. E.g.

    • Day 1: if you specified <PackageReference Include="My.Sample.Lib" Version="4.0.0"/> but the versions available on the NuGet repositories were 4.1.0, 4.2.0 and 4.3.0. In this case, NuGet would have resolved to 4.1.0 (nearest minimum version)

    • Day 2: Version 4.0.0 gets published. NuGet will now find the exact match and start resolving to 4.0.0

  • A given package version is removed from the repository. Though nuget.org does not allow package deletions, not all package repositories have this constraints. This results in NuGet finding the best match when it cannot resolve to the deleted version.

Enabling lock file

In order to persist the full closure of package dependencies you can opt-in to the lock file feature by setting the MSBuild property RestorePackagesWithLockFile for your project:

<PropertyGroup>
    <!--- ... -->
    <RestorePackagesWithLockFile>true</RestorePackagesWithLockFile>
    <!--- ... -->
</PropertyGroup>    

If this property is set, NuGet restore will generate a lock file - packages.lock.json file at the project root directory that lists all the package dependencies.

Note

Once a project has packages.lock.json file in its root directory, the lock file is always used with restore even if the property RestorePackagesWithLockFile is not set. So another way to opt-in to this feature is to create a dummy blank packages.lock.json file in the project's root directory.

restore behavior with lock file

If a lock file is present for project, NuGet uses this lock file to run restore. NuGet does a quick check to see if there were any changes in the package dependencies as mentioned in the project file (or dependent projects' files) and if there were no changes it just restores the packages mentioned in the lock file. There is no re-evaluation of package dependencies.

If NuGet detects a change in the defined dependencies as mentioned in the project file(s), it re-evaluates the package graph and updates the lock file to reflect the new package closure for the project.

For CI/CD and other scenarios, where you would not want to change the package dependencies on the fly, you can do so by setting the lockedmode to true:

For dotnet.exe, run:

> dotnet.exe restore --locked-mode

For msbuild.exe, run:

> msbuild.exe -t:restore -p:RestoreLockedMode=true

You may also set this conditional MSBuild property in your project file:

<PropertyGroup>
    <!--- ... -->
    <RestoreLockedMode>true</RestoreLockedMode>
    <!--- ... -->
</PropertyGroup> 

If locked mode is true, restore will either restore the exact packages as listed in the lock file or fail if you updated the defined package dependencies for the project after lock file was created.

Make lock file part of your source repository

If you are building an application, an executable and the project in question is at the start of the dependency chain then do check in the lock file to the source code repository so that NuGet can make use of it during restore.

However, if your project is a library project that you do not ship or a common code project on which other projects depend upon, you should not check in the lock file as part of your source code. There is no harm in keeping the lock file but the locked package dependencies for the common code project may not be used, as listed in the lock file, during the restore/build of a project that depends on this common-code project.

Eg.

ProjectA
  |------> PackageX 2.0.0
  |------> ProjectB
             |------>PackageX 1.0.0

If ProjectA has a dependency on a PackageX version 2.0.0 and also references ProjectB that depends on PackageX version 1.0.0, then the lock file for ProjectB will list a dependency on PackageX version 1.0.0. However, when ProjectA is built, its lock file will contain a dependency on PackageX version 2.0.0 and not 1.0.0 as listed in the lock file for ProjectB. Thus, the lock file of a common code project has little say over the packages resolved for projects that depend on it.

Lock file extensibility

You can control various behaviors of restore with lock file as described below:

Option MSBuild equivalent option
--use-lock-file Bootstraps use of lock file for a project. You can alternatively set RestorePackagesWithLockFile property in the project file
--locked-mode Enables locked mode for restore. This is useful in CI/CD scenarios where you would like to get the repeatable builds. This can be also by setting the RestoreLockedMode MSBuild property to true
--force-evaluate This option is useful with packages with floating version defined in the project. By default, NuGet restore will not update the package version automatically upon each restore unless you run restore with --force-evaluate option.
--lock-file-path Defines a custom lock file location for a project. This can be also achieved by setting the MSBuild property NuGetLockFilePath. By default, NuGet supports packages.lock.json at the root directory. If you have multiple projects in the same directory, NuGet supports project specific lock file packages.<project_name>.lock.json