In Entity framework 6, It throws multiple identity columns error even though I have one primary key

I am new to MVC and I am trying to design database using code-first approach. I have read the following thread: Entity Framework 5 Multiple identity columns specified for table. Only one identity column per table is allowed But I believe this is for previous MVC as the current one does not have the following methods as explained the author of the answer. I am getting following error :

PM> update-database
Cannot determine a valid start-up project. Using project 'Project_Zyoos' instead. Your configuration file and working directory

may not be set as expected. Use the -StartUpProjectName parameter to set one explicitly. Use the -Verbose switch for more information. Specify the '-Verbose' flag to view the SQL statements being applied to the target database. No pending explicit migrations. Applying automatic migration: 201804030625539_AutomaticMigration. System.Data.SqlClient.SqlException (0x80131904): Multiple identity columns specified for table 'Tournament'. Only one identity column per table is allowed. at System.Data.SqlClient.SqlConnection.OnError(SqlException exception, Boolean breakConnection, Action1 wrapCloseInAction) at System.Data.SqlClient.SqlInternalConnection.OnError(SqlException exception, Boolean breakConnection, Action1 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.RunExecuteNonQueryTds(String methodName, Boolean async, Int32 timeout, Boolean asyncWrite) at System.Data.SqlClient.SqlCommand.InternalExecuteNonQuery(TaskCompletionSource1 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, DbCommandInterceptionContext1 c) at System.Data.Entity.Infrastructure.Interception.InternalDispatcher1.Dispatch[TTarget,TInterceptionContext,TResult](TTarget target, Func3 operation, TInterceptionContext interceptionContext, Action3 executing, Action3 executed) at System.Data.Entity.Infrastructure.Interception.DbCommandDispatcher.NonQuery(DbCommand command, DbCommandInterceptionContext interceptionContext) at System.Data.Entity.Internal.InterceptableDbCommand.ExecuteNonQuery() at System.Data.Entity.Migrations.DbMigrator.ExecuteSql(MigrationStatement migrationStatement, DbConnection connection, DbTransaction transaction, DbInterceptionContext interceptionContext) at System.Data.Entity.Migrations.Infrastructure.MigratorLoggingDecorator.ExecuteSql(MigrationStatement migrationStatement, DbConnection connection, DbTransaction transaction, DbInterceptionContext interceptionContext) at System.Data.Entity.Migrations.DbMigrator.ExecuteStatementsInternal(IEnumerable1 migrationStatements, DbConnection connection, DbTransaction transaction, DbInterceptionContext interceptionContext) at System.Data.Entity.Migrations.DbMigrator.ExecuteStatementsWithinTransaction(IEnumerable1 migrationStatements, DbTransaction transaction, DbInterceptionContext interceptionContext) at System.Data.Entity.Migrations.DbMigrator.ExecuteStatementsWithinNewTransaction(IEnumerable1 migrationStatements, DbConnection connection, DbInterceptionContext interceptionContext) at System.Data.Entity.Migrations.DbMigrator.ExecuteStatementsInternal(IEnumerable1 migrationStatements, DbConnection connection, DbInterceptionContext interceptionContext) at System.Data.Entity.Migrations.DbMigrator.ExecuteStatementsInternal(IEnumerable1 migrationStatements, DbConnection connection) at System.Data.Entity.Migrations.DbMigrator.<>c__DisplayClass30.<ExecuteStatements>b__2e() at System.Data.Entity.SqlServer.DefaultSqlExecutionStrategy.<>c__DisplayClass1.<Execute>b__0() at System.Data.Entity.SqlServer.DefaultSqlExecutionStrategy.Execute[TResult](Func1 operation) at System.Data.Entity.SqlServer.DefaultSqlExecutionStrategy.Execute(Action operation) at System.Data.Entity.Migrations.DbMigrator.ExecuteStatements(IEnumerable1 migrationStatements, DbTransaction existingTransaction) at System.Data.Entity.Migrations.DbMigrator.ExecuteStatements(IEnumerable1 migrationStatements) at System.Data.Entity.Migrations.Infrastructure.MigratorBase.ExecuteStatements(IEnumerable1 migrationStatements) at System.Data.Entity.Migrations.DbMigrator.ExecuteOperations(String migrationId, VersionedModel targetModel, IEnumerable1 operations, IEnumerable1 systemOperations, Boolean downgrading, Boolean auto) at System.Data.Entity.Migrations.DbMigrator.AutoMigrate(String migrationId, VersionedModel sourceModel, VersionedModel targetModel, Boolean downgrading) at System.Data.Entity.Migrations.Infrastructure.MigratorLoggingDecorator.AutoMigrate(String migrationId, VersionedModel sourceModel, VersionedModel targetModel, Boolean downgrading) at System.Data.Entity.Migrations.DbMigrator.Upgrade(IEnumerable1 pendingMigrations, String targetMigrationId, String lastMigrationId) at System.Data.Entity.Migrations.Infrastructure.MigratorLoggingDecorator.Upgrade(IEnumerable`1 pendingMigrations, String targetMigrationId, String lastMigrationId) at System.Data.Entity.Migrations.DbMigrator.UpdateInternal(String targetMigration) at System.Data.Entity.Migrations.DbMigrator.<>c__DisplayClassc.b__b() at System.Data.Entity.Migrations.DbMigrator.EnsureDatabaseExists(Action mustSucceedToKeepDatabase) at System.Data.Entity.Migrations.Infrastructure.MigratorBase.EnsureDatabaseExists(Action mustSucceedToKeepDatabase) at System.Data.Entity.Migrations.DbMigrator.Update(String targetMigration) at System.Data.Entity.Migrations.Infrastructure.MigratorBase.Update(String targetMigration) at System.Data.Entity.Migrations.Design.ToolingFacade.UpdateRunner.Run() at System.AppDomain.DoCallBack(CrossAppDomainDelegate callBackDelegate) at System.AppDomain.DoCallBack(CrossAppDomainDelegate callBackDelegate) at System.Data.Entity.Migrations.Design.ToolingFacade.Run(BaseRunner runner) at System.Data.Entity.Migrations.Design.ToolingFacade.Update(String targetMigration, Boolean force) at System.Data.Entity.Migrations.UpdateDatabaseCommand.<>c__DisplayClass2.<.ctor>b__0() at System.Data.Entity.Migrations.MigrationsDomainCommand.Execute(Action command) ClientConnectionId:7c9c5b36-8178-4bf9-bade-80c33d43103f Error Number:2744,State:2,Class:16 Multiple identity columns specified for table 'Tournament'. Only one identity column per table is allowed. Code is writtern below:

using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;
using System.Linq;
using System.Web;

namespace Project_Zyoos.Entities
{
    [Table("Tournament")]
    public class Tournament
    {
        [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
        [Key]
        public int Tournament_Id { get; set; }
        [MaxLength(255)][Required]
        public string Tournament_Title { get; set; }
        [MaxLength(2048)]
        public string Tournament_Description { get; set; }


    }
}

Thanks in Advance. :)

It seems like startup project is conflicting may be you have to choose the Default project name to current project(a small dropdown box top of command prompt in nuget package manager) and then update your database through update command or else you have to specify all you parameter manually bellow command:

Update-Database [-SourceMigration <String>] [-TargetMigration <String>] [- 
Script] [-Force] 
[-ProjectName <String>] [-StartUpProjectName <String>] [- 
ConfigurationTypeName <String>] 
-ConnectionString <String> -ConnectionProviderName <String> 
[-AppDomainBaseDirectory <String>] [<CommonParameters>]

Description Updates the database to the current model by applying pending migrations.

Parameters -SourceMigration Only valid with -Script. Specifies the name of a particular migration to use as the update’s starting point. If ommitted, the last applied migration in the database will be used.

-TargetMigration Specifies the name of a particular migration to update the database to. If ommitted, the current model will be used.

-Script Generate a SQL script rather than executing the pending changes directly.

-Force Specifies that data loss is acceptable during automatic migration of the database.

-ProjectName Specifies the project that contains the migration configuration type to be used. If ommitted, the default project selected in package manager console is used.

-StartUpProjectName Specifies the configuration file to use for named connection strings. If omitted, the specified project’s configuration file is used.

-ConfigurationTypeName Specifies the migrations configuration to use. If omitted, migrations will attempt to locate a single migrations configuration type in the target project.

-ConnectionStringName Specifies the name of a connection string to use from the application’s configuration file.

-ConnectionString Specifies the the connection string to use. If omitted, the context’s default connection will be used.

-ConnectionProviderName Specifies the provider invariant name of the connection string.

-AppDomainBaseDirectory Specifies the directory to use for the app-domain that is used for running Migrations code such that the app-domain is able to find all required assemblies. This is an advanced option that should only be needed if the solution contains several projects such that the assemblies needed for the context and configuration are not all referenced from either the project containing the context or the project containing the migrations. This cmdlet supports the common parameters: Verbose, Debug, ErrorAction, ErrorVariable, WarningAction, WarningVariable, OutBuffer, PipelineVariable, and OutVariable.

you can also get help like in package manager console:

 get-help Update-Database -full