Require unique phone number in Asp.Net Core Identity

Question

In Asp.Net Core Identity framework, I can easily require a unique email address by setting RequireUniqueEmail = true.

Is there any way to do the same for the user's phone number? Note that I don't want to require a confirmed phone number to sign in. The user is not required to enter a phone number but if they do, it must be unique.

Answer 1

You can try this, basically enforce it at the Db level first, followed by implementing proper checks at the Manager level.

At DbContext, I declared the indexing and uniqueness of both the username and email properties.

taken from the link

    // ================== Customizing IdentityCore Tables ================== //

            builder.Entity<User>().ToTable("Users").Property(p => p.Id).HasColumnName("Id").ValueGeneratedOnAdd();
            builder.Entity<User>(entity =>
            {
                entity.HasIndex(u => u.UserName).IsUnique();
                entity.HasIndex(u => u.NormalizedUserName).IsUnique();
                entity.HasIndex(u => u.Email).IsUnique();
                entity.HasIndex(u => u.NormalizedEmail).IsUnique();

                entity.Property(u => u.Rating).HasDefaultValue(0).IsRequired();
                entity.HasMany(u => u.UserRoles).WithOne(ur => ur.User)
                    .HasForeignKey(ur => ur.UserId).OnDelete(DeleteBehavior.Restrict);
                entity.HasMany(u => u.UserClaims).WithOne(uc => uc.User)
                    .HasForeignKey(uc => uc.UserId).OnDelete(DeleteBehavior.Restrict);
            });

And for the Manager level code:

    /// <summary>
            /// Sets the <paramref name="email"/> address for a <paramref name="user"/>.
            /// </summary>
            /// <param name="user">The user whose email should be set.</param>
            /// <param name="email">The email to set.</param>
            /// <returns>
            /// The <see cref="Task"/> that represents the asynchronous operation, containing the <see cref="IdentityResult"/>
            /// of the operation.
            /// </returns>
            public override async Task<IdentityResult> SetEmailAsync(User user, string email)
            {
                var dupeUser = await FindByEmailAsync(email);
    
                if (dupeUser != null)
                {
                    return IdentityResult.Failed(new IdentityError() {
                        Code = "DuplicateEmailException", // Wrong practice, lets set some beautiful code values in the future
                        Description = "An existing user with the new email already exists."
                    });
                }
    
                // Perform dupe checks
    
                // Code that runs in SetEmailAsync
                // Adapted from: aspnet/Identity/blob/dev/src/Core/UserManager.cs
                //
                // ThrowIfDisposed();
                // var store = GetEmailStore();
                // if (user == null)
                // {
                //     throw new ArgumentNullException(nameof(user));
                // }
    
                // await store.SetEmailAsync(user, email, CancellationToken);
                // await store.SetEmailConfirmedAsync(user, false, CancellationToken);
                // await UpdateSecurityStampInternal(user);
    
                //return await UpdateUserAsync(user);
    
                return await base.SetEmailAsync(user, email);
            }

This way, we retain .NET Core Identity Code's Integrity while enforcing the uniqueness of the property/properties that we want.

Note that the samples above are for email as of now. Simply do the same and then instead of modifying SetEmailAsync, work on SetPhoneNumberAsync at UserManager.cs.