Azure .NET后端SaveChanges()验证失败问题求助（Xamarin.iOS）

Hey, let's break down why that salt value is ending up as null in your database when saving new users to your Azure Mobile Services .NET backend. I've run into similar issues with EF and mobile service entity handling before, so here are the most likely culprits to check:

1. Double-check your salt assignment logic #

First off, make sure you're actually assigning the generated salt to your user entity before calling SaveChanges(). It sounds obvious, but it's easy to accidentally put the assignment after the save call, or mix up variable names (like assigning to a local salt variable instead of the entity's Salt property).

For example, if your user entity is named AppUser, you need something like this:

var generatedSalt = CreateSalt(); // Your salt generation method
var newUser = new AppUser
{
    Username = model.Username,
    Salt = generatedSalt, // Don't skip this line!
    HashedPassword = HashPassword(model.Password, generatedSalt)
};

dbContext.AppUsers.Add(newUser);
await dbContext.SaveChangesAsync(); // Salt is set BEFORE this call

2. Verify your EF entity and database configuration #

Next, check if your User entity's Salt property is properly mapped to the database:

• Is the Salt property marked as non-nullable in your entity? If your database table has Salt as a required (non-null) column, make sure your entity has the [Required] attribute or is configured in EF to be non-nullable. If EF thinks it's optional, it might not flag a missing value until it hits the database.
• Are the property name and database column name aligned? If your database column is named SaltValue but your entity property is Salt, you'll need to add a [Column("SaltValue")] attribute to the property so EF maps it correctly.

3. Check if something is overwriting the salt before save #

It's possible that after you assign the salt, another piece of code is resetting it to null. Look for any logic between the salt assignment and SaveChanges() that modifies the user entity. This could be:

• An async operation that accidentally reinitializes the entity
• A custom EntityDomainManager or Azure Mobile Services interceptor that manipulates entities before saving
• A validation method that resets properties incorrectly

4. Validate your salt generation method #

Make sure your salt generation function is actually returning a non-null value. For example, if you're using RNGCryptoServiceProvider, double-check that you're converting the byte array to a string correctly (like using Convert.ToBase64String() which won't return null if the byte array is valid). Add a quick debug check to confirm:

var generatedSalt = CreateSalt();
Debug.Assert(generatedSalt != null, "Salt generation failed - returned null!");

5. Debug the save process with EF logging #

Turn on EF logging to see exactly what SQL is being sent to the database. This will tell you if the salt value is even being included in the INSERT statement. If it's missing, that confirms the issue is in your code before the save; if it's present but still showing as null in the DB, you might have a database-level constraint or trigger overriding it.

Hopefully one of these points hits the mark. If you can share more snippets of your salt generation or entity assignment code, I can help narrow it down further!

内容的提问来源于stack exchange，提问作者naffie