已经输入Install-Package EntityFramework.Commands –Pre，但是当我尝试Add-Migration Initial时，我收到以下错误：
The EntityFramework package is not installed on project '…'.
作为另一个线索，当我尝试Use-DbContext命令时，我也会收到错误。这是我的包管理器控制台会话：
PM> Install-Package EntityFramework.Commands –Pre
Package 'EntityFramework.Commands.7.0.0-rc1-final' already exists in project '…'
PM> Add-Migration Initial
The EntityFramework package is not installed on project '…'.
PM> Use-DbContext
Use-DbContext : The term 'Use-DbContext' is not recognized as the name of a cmdlet, function, script file, or operable program. Check the spelling of the name, or if a path was included, verify
that the path is correct and try again.
At line:1 char:1
+ Use-DbContext
+ ~~~~~~~~~~~~~
+ CategoryInfo : ObjectNotFound: (Use-DbContext:String) [], CommandNotFoundException
+ FullyQualifiedErrorId : CommandNotFoundException
我做错了什么？