无法从OWIN Identity表读取数据问题求助

Hey there, let's work through why your query is returning null even though you know the user exists in the shared database. Here are some practical checks to narrow down the issue:

• Case sensitivity mismatch
  Many databases (like SQL Server with case-sensitive collation) treat john@example.com and John@Example.com as different values. Try adjusting your query to ignore case first:

  var user = usercontext.Users
                        .Where(x => x.Username.Equals(Login_.Email, StringComparison.OrdinalIgnoreCase))
                        .FirstOrDefault();
  

  You can also verify your database's collation setting—look for CI_AS (case-insensitive) vs CS_AS (case-sensitive) on the Username column or the entire table.

• Entity Framework mapping errors
  Double-check that your DbContext is correctly mapped to the Identity table:

  • If you renamed the default AspNetUsers table, make sure you’ve added the [Table("YourCustomTableName")] attribute to your IdentityUser subclass, or configured it via Fluent API.
  • Confirm the Username property in your user class maps to the correct column in the database (sometimes teams use Email as the username column, so you might need to query x.Email == Login_.Email instead).

• Wrong connection string
  It’s easy to accidentally point your usercontext to a local test database instead of the shared one. Debug your connection string (print it to the console or debug window) and cross-verify it with the connection details you use to access the shared database directly.

• DbContext caching interference
  Entity Framework caches entities it’s already fetched, which might be returning an outdated null result. Bypass the cache with AsNoTracking() to pull fresh data from the database:

  var user = usercontext.Users
                        .AsNoTracking()
                        .Where(x => x.Username == Login_.Email)
                        .FirstOrDefault();
  

• Soft-deleted or inactive users
  If your application uses soft deletion (e.g., an IsDeleted flag) or user status flags (like IsActive), make sure your query isn’t filtering out the existing user. Add a check like && !x.IsDeleted if applicable.

• Raw SQL sanity check
  Run the equivalent SQL query directly against the database (using SSMS, pgAdmin, etc.) to confirm the user exists:

  SELECT * FROM AspNetUsers WHERE Username = 'your-login-email-here';
  

  If this returns the user but your EF query doesn’t, the problem is definitely in your EF configuration. If it doesn’t return the user, the registration process might not have saved the user correctly to the shared database.

Start with these steps—they cover most of the common gotchas with Identity user queries. Let me know if you hit a wall with any of these!

内容的提问来源于stack exchange，提问作者John Nyingi