如何解决“违反UNIQUE KEY约束”

Question

I am using Entity Framework to Add a User to the database. When I add the first user to the database, it works. When I try to add another user to the database, I get the error : System.Data.SqlClient.SqlException: Violation of UNIQUE KEY constraint

I'm not too sure what I am doing here. I've even made an IF Condition to check weather the key is unique but the actual error messages saying i'm inserting a duplicate key.

So here is my current code:

//Create new GUID
string newGuid = Guid.NewGuid().ToString();

//Checking if Primary Key already exists in table
if (!context.Users_tbl.Any(u => u.UserID == newGuid))
{

//Installise New User Class
var user = new Users_tbl()
{
UserID = newGuid,
Email = email,
Password = AESCrypt.Encrypt(password),
};

//Add User to ADO and Commit Changes
context.Users_tbl.Add(user);
context.SaveChanges();

//Find UserID via Email
var userID = context.Users_tbl.Where(p => p.Email == email).Select(p => p.UserID).FirstOrDefault();

//Installise New UserInfo Class
var usersInfo = new UsersInfo_tbl()
{
FKUserID = userID,
FirstName = firstName,
LastName = lastName
};

//Add User to ADO and Commit Changes
context.UsersInfo_tbl.Add(usersInfo);
context.SaveChanges();

//Send Activation Link via Email
SendActivationEmail(userID);

//Set Session ID
Session["UserID"] = userID;
Response.Redirect("/Dashboard/DashBoard.aspx", false);
}

Below is the exact error message I am getting.

System.Data.Entity.Infrastructure.DbUpdateException: An error occurred while updating the entries. See the inner exception for details. ---> System.Data.Entity.Core.UpdateException: An error occurred while updating the entries. See the inner exception for details. ---> System.Data.SqlClient.SqlException: Violation of UNIQUE KEY constraint 'UQ__Users_tb__2B5B96C51C3AA70E'. Cannot insert duplicate key in object 'dbo.Users_tbl'. The duplicate key value is (<NULL>).
The statement has been terminated.
   at System.Data.SqlClient.SqlConnection.OnError(SqlException exception, Boolean breakConnection, Action`1 wrapCloseInAction)
   at System.Data.SqlClient.SqlInternalConnection.OnError(SqlException exception, Boolean breakConnection, Action`1 wrapCloseInAction)
   at System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning(TdsParserStateObject stateObj, Boolean callerHasConnectionLock, Boolean asyncClose)
   at System.Data.SqlClient.TdsParser.TryRun(RunBehavior runBehavior, SqlCommand cmdHandler, SqlDataReader dataStream, BulkCopySimpleResultSet bulkCopyHandler, TdsParserStateObject stateObj, Boolean& dataReady)
   at System.Data.SqlClient.SqlCommand.FinishExecuteReader(SqlDataReader ds, RunBehavior runBehavior, String resetOptionsString, Boolean isInternal, Boolean forDescribeParameterEncryption, Boolean shouldCacheForAlwaysEncrypted)
   at System.Data.SqlClient.SqlCommand.RunExecuteReaderTds(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, Boolean async, Int32 timeout, Task& task, Boolean asyncWrite, Boolean inRetry, SqlDataReader ds, Boolean describeParameterEncryptionRequest)
   at System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method, TaskCompletionSource`1 completion, Int32 timeout, Task& task, Boolean& usedCache, Boolean asyncWrite, Boolean inRetry)
   at System.Data.SqlClient.SqlCommand.InternalExecuteNonQuery(TaskCompletionSource`1 completion, String methodName, Boolean sendToPipe, Int32 timeout, Boolean& usedCache, Boolean asyncWrite, Boolean inRetry)
   at System.Data.SqlClient.SqlCommand.ExecuteNonQuery()
   at System.Data.Entity.Infrastructure.Interception.DbCommandDispatcher.<NonQuery>b__0(DbCommand t, DbCommandInterceptionContext`1 c)
   at System.Data.Entity.Infrastructure.Interception.InternalDispatcher`1.Dispatch[TTarget,TInterceptionContext,TResult](TTarget target, Func`3 operation, TInterceptionContext interceptionContext, Action`3 executing, Action`3 executed)
   at System.Data.Entity.Infrastructure.Interception.DbCommandDispatcher.NonQuery(DbCommand command, DbCommandInterceptionContext interceptionContext)
   at System.Data.Entity.Internal.InterceptableDbCommand.ExecuteNonQuery()
   at System.Data.Entity.Core.Mapping.Update.Internal.DynamicUpdateCommand.Execute(Dictionary`2 identifierValues, List`1 generatedValues)
   at System.Data.Entity.Core.Mapping.Update.Internal.UpdateTranslator.Update()
   --- End of inner exception stack trace ---
   at System.Data.Entity.Core.Mapping.Update.Internal.UpdateTranslator.Update()
   at System.Data.Entity.Core.EntityClient.Internal.EntityAdapter.<Update>b__2(UpdateTranslator ut)
   at System.Data.Entity.Core.EntityClient.Internal.EntityAdapter.Update[T](T noChangesResult, Func`2 updateFunction)
   at System.Data.Entity.Core.EntityClient.Internal.EntityAdapter.Update()
   at System.Data.Entity.Core.Objects.ObjectContext.<SaveChangesToStore>b__35()
   at System.Data.Entity.Core.Objects.ObjectContext.ExecuteInTransaction[T](Func`1 func, IDbExecutionStrategy executionStrategy, Boolean startLocalTransaction, Boolean releaseConnectionOnSuccess)
   at System.Data.Entity.Core.Objects.ObjectContext.SaveChangesToStore(SaveOptions options, IDbExecutionStrategy executionStrategy, Boolean startLocalTransaction)
   at System.Data.Entity.Core.Objects.ObjectContext.<>c__DisplayClass2a.<SaveChangesInternal>b__27()
   at System.Data.Entity.SqlServer.DefaultSqlExecutionStrategy.Execute[TResult](Func`1 operation)
   at System.Data.Entity.Core.Objects.ObjectContext.SaveChangesInternal(SaveOptions options, Boolean executeInExistingTransaction)
   at System.Data.Entity.Core.Objects.ObjectContext.SaveChanges(SaveOptions options)
   at System.Data.Entity.Internal.InternalContext.SaveChanges()
   --- End of inner exception stack trace ---
   at System.Data.Entity.Internal.InternalContext.SaveChanges()
   at System.Data.Entity.Internal.LazyInternalContext.SaveChanges()
   at System.Data.Entity.DbContext.SaveChanges()
   at ReapStreamV2.Auth.Signup.SignUp.Submit_Click(Object sender, EventArgs e) in C:\Users\Milan\Documents\ReapStream DEV\ReapStream\ReapStreamV2\Auth\Signup\SignUp.aspx.cs:line 123

My Primary Key is Unique;

```
CREATE TABLE [dbo].[Users_tbl] (
    [UserID]            NVARCHAR (128) NOT NULL,
    [Email]             VARCHAR (255)  NOT NULL,
    [Password]          VARCHAR (255)  NOT NULL,
    [IsTwoFAEnabled]    BIT            NOT NULL,
    [TwoFACode]         NVARCHAR (128) NULL,
    [hasActivated]      BIT            NOT NULL,
    [AccessFailedCount] INT            NOT NULL,
    CONSTRAINT [PK__Users_tb__1788CCAC29DEB237] PRIMARY KEY CLUSTERED ([UserID] ASC),
    CONSTRAINT [UQ__Users_tb__2B5B96C51C3AA70E] UNIQUE NONCLUSTERED ([TwoFACode] ASC)
);

```

Answer 1

The error message states "Violation of UNIQUE KEY constraint 'UQ__Users_tb__2B5B96C51C3AA70E'. Cannot insert duplicate key in object 'dbo.Users_tbl'. The duplicate key value is (<NULL>)."

Looking at the lower part of your message I see the UQ__Users_tb__2B5B96C51C3AA70E relates to the TwoFACode field.

In the code adding the user to the table, you have not populated this field - hence violating the unique constraint with two null entries.

" [TwoFACode] NVARCHAR (128) NULL " - the field is allowed to be null - but there can only be one null field due to the constraint.

Answer 2

To go into more detail of PaulF's comments:

var usersInfo = new UsersInfo_tbl()
{
    FKUserID = userID,
    FirstName = firstName,
    LastName = lastName
};

This sets the FKUserID , but you haven't set the ID for this table, so you are trying to insert a null value, which is what the error is telling you: The duplicate key value is (<NULL>). The key to note here is that it's the UsersInfo_tbl table, not the Users_tbl table. Since you haven't included the schema for the UsersInfo_tbl table, we don't know what the primary is for that, or if it allows null. If it does (which it seems like it does), it shouldn't. Try looking at the data of both tables to see exactly what's going on.

This also says that there's already a null value in your table, which most likely needs to be updated with a real value.

As a side note, I find adding "tbl" to a table name to be fairly atrocious. Aside from the look & feel of it being bad, it can lead to problems later. Other people find it to be bad practice as well.

https://dba.stackexchange.com/questions/154251/is-adding-the-tbl-prefix-to-table-names-really-a-problem

Answer 3

IMHO You should make sure 'Email' column is unique becouse now you could get more then one user (there is a change userID will be random if there will be more users with same Email in database and you ask for First one):

 //Find UserID via Email var userID = context.Users_tbl.Where(p => p.Email == email).Select(p => p.UserID).FirstOrDefault(); 

Make sure you are using Find() method from EntityFramework library with will get user by Id key (it will fetch data from context first instead of making trip to database) instead of query database with Where() linq method.

If your code is scope of one method than you don't have to ask context or database if user exists but set 'FKUserID' property from 'UsersInfo_tbl' with newGuid value.

Answer 4

Its a bad practice to try setting the guid in code populate the rest of the object (excluding the guid).

var user = new Users_tbl()
{
//UserID = newGuid, You dont need this.
Email = email,
Password = AESCrypt.Encrypt(password),
};

YourRepository.SaveChanges();
var userId = user.UserId; (this should retrieve the guid back).

Also your UserId in the table shouldn't be nvarchar but UniqueIdentifer

Open your table in SSMS and you could set default value for your guid

Or run the command to change it for you.

ALTER TABLE dbo.Users_tbl
   ALTER [UserId] UNIQUEIDENTIFIER DEFAULT NEWID() PRIMARY KEY;