FindByNameAsync vs FindByIdAsync vs FindByEmailAsync vs FindByLoginAsync

In ASP.NET Identity, UserManager is a core class that provides a set of APIs to manage user accounts. The methods you mentioned (FindByNameAsync, FindByIdAsync, FindByEmailAsync, and FindByLoginAsync) are used to find a user based on different criteria. These methods help you retrieve user information from the underlying database table, usually named AspNetUsers.

Here's how they map to columns in the database table:

1. FindByNameAsync: This method searches for a user by their username or user name. The username is typically a unique identifier for a user. In the database table, this usually maps to the UserName column.

2. FindByIdAsync: This method searches for a user by their unique identifier, which is usually a GUID. In the database table, this maps to the Id column.

3. FindByEmailAsync: This method searches for a user by their email address. In the database table, this maps to the Email column.

4. FindByLoginAsync: This method searches for a user based on a specified external login provider and its unique identifier. In the database, external login information is stored in the AspNetUserLogins table, which has columns for the LoginProvider and ProviderKey. This method allows you to find a user by specifying these two values.

前面三个方法查询的数据在AspNetUsers表，FindByLogin方法查询的数据在AspNetUserLogins表