EF - "Update-Database" causing Sequence contains more than one element

Question

I have just finished modifying my models, ran "Update-Database" in the package manager console and BOOM! I received a "Sequence contains more than one element" error. Upon scanning through the console, it did say No pending explicit migrations. which is obviously wrong since I renamed some models. I also found a SingleOrDefault call I don't know where it came from. I commented out my seed method so that's not causing it

    No pending explicit migrations.
System.InvalidOperationException: Sequence contains more than one element
   at System.Linq.Enumerable.SingleOrDefault[TSource](IEnumerable`1 source)
   at System.Data.Entity.Migrations.Infrastructure.EdmModelDiffer.<>c__DisplayClass280.<IndexesEqual>b__27d(String c)
   at System.Linq.Enumerable.<>c__DisplayClass7_0`3.<CombineSelectors>b__0(TSource x)
   at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
   at System.Linq.Enumerable.SequenceEqual[TSource](IEnumerable`1 first, IEnumerable`1 second, IEqualityComparer`1 comparer)
   at System.Data.Entity.Migrations.Infrastructure.EdmModelDiffer.IndexesEqual(ConsolidatedIndex consolidatedIndex1, ConsolidatedIndex consolidatedIndex2, ICollection`1 renamedColumns)
   at System.Data.Entity.Migrations.Infrastructure.EdmModelDiffer.<>c__DisplayClass271.<FindAddedIndexes>b__26d(ConsolidatedIndex i1, ConsolidatedIndex i2)
   at System.Data.Entity.Utilities.DynamicEqualityComparer`1.Equals(T x, T y)
   at System.Linq.Set`1.Find(TElement value, Boolean add)
   at System.Linq.Enumerable.<ExceptIterator>d__72`1.MoveNext()
   at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
   at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
   at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
   at System.Data.Entity.Migrations.Infrastructure.EdmModelDiffer.Diff(ModelMetadata source, ModelMetadata target, Lazy`1 modificationCommandTreeGenerator, MigrationSqlGenerator migrationSqlGenerator, String sourceModelVersion, String targetModelVersion)
   at System.Data.Entity.Migrations.Infrastructure.EdmModelDiffer.Diff(XDocument sourceModel, XDocument targetModel, Lazy`1 modificationCommandTreeGenerator, MigrationSqlGenerator migrationSqlGenerator, String sourceModelVersion, String targetModelVersion)
   at System.Data.Entity.Migrations.DbMigrator.IsModelOutOfDate(XDocument model, DbMigration lastMigration)
   at System.Data.Entity.Migrations.DbMigrator.Upgrade(IEnumerable`1 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.<Update>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)
Sequence contains more than one element

EDIT After some digging, found out that the error occurs when EF queries the _MigrationHistory table. but shouldn't it expect records since I want to update the schema?

Also, does moving the models to another project have an effect?

EDIT AGAIN I got tired of finding what is causing the problem so I did a quick workaround

1. Create a backup script of the data
2. Delete the current database
3. ran Add-Migration and Update-Database in the console
4. Renamed the table names in the backup script accordingly
5. Ran the script

All is working fine now. Just have to figure out why loading is sooooooooooooo annoyingly slow

Answer 1

This usually happens to me when I have duplicate entries in my database, corresponding to the same entity.

Deleting the duplicates makes it work. If you have the data script with you please check and confirm if there were duplicate records in the entities you tried to update in your migration script.