'Sequence contains no matching element' scaffolding database tables

Steps to reproduce

dotnet ef dbcontext scaffold "connect string" "Pomelo.EntityFrameworkCore.MySql" --verbose

The issue

Throws an exception after not finding design-time services.

Using project 'd:\Client\olab\devel\repos\OLab4\OLab4-api\Service\OLabWebAPI.csproj'.
Using startup project 'd:\Client\olab\devel\repos\OLab4\OLab4-api\Service\OLabWebAPI.csproj'.
Writing 'd:\Client\olab\devel\repos\OLab4\OLab4-api\Service\obj\OLabWebAPI.csproj.EntityFrameworkCore.targets'...
dotnet msbuild /target:GetEFProjectMetadata /property:EFProjectMetadataFile=C:\Users\corey\AppData\Local\Temp\tmp3401.tmp /verbosity:quiet /nologo d:\Client\olab\devel\repos\OLab4\OLab4-api\Service\OLabWebAPI.csproj
Writing 'd:\Client\olab\devel\repos\OLab4\OLab4-api\Service\obj\OLabWebAPI.csproj.EntityFrameworkCore.targets'...
dotnet msbuild /target:GetEFProjectMetadata /property:EFProjectMetadataFile=C:\Users\corey\AppData\Local\Temp\tmp35D7.tmp /verbosity:quiet /nologo d:\Client\olab\devel\repos\OLab4\OLab4-api\Service\OLabWebAPI.csproj
Build started...
dotnet build d:\Client\olab\devel\repos\OLab4\OLab4-api\Service\OLabWebAPI.csproj /verbosity:quiet /nologo

Build succeeded.
    0 Warning(s)
    0 Error(s)

Time Elapsed 00:00:01.93
Build succeeded.
dotnet exec --depsfile d:\Client\olab\devel\repos\OLab4\OLab4-api\Service\bin\Debug\netcoreapp3.1\OLabWebAPI.deps.json --additionalprobingpath C:\Users\corey\.nuget\packages --runtimeconfig d:\Client\olab\devel\repos\OLab4\OLab4-api\Service\bin\Debug\netcoreapp3.1\OLabWebAPI.runtimeconfig.json C:\Users\corey\.dotnet\tools\.store\dotnet-ef\5.0.0\dotnet-ef\5.0.0\tools\netcoreapp3.1\any\tools\netcoreapp2.0\any\ef.dll dbcontext scaffold server=diskstation.local;uid=entrada_dev;pwd=b012db9d53B!;database=dev_olab Pomelo.EntityFrameworkCore.MySql --assembly d:\Client\olab\devel\repos\OLab4\OLab4-api\Service\bin\Debug\netcoreapp3.1\OLabWebAPI.dll --startup-assembly d:\Client\olab\devel\repos\OLab4\OLab4-api\Service\bin\Debug\netcoreapp3.1\OLabWebAPI.dll --project-dir d:\Client\olab\devel\repos\OLab4\OLab4-api\Service\ --language C# --working-dir d:\Client\olab\devel\repos\OLab4\OLab4-api\Service --verbose --root-namespace OLabWebAPI
Using assembly 'OLabWebAPI'.
Using startup assembly 'OLabWebAPI'.
Using application base 'd:\Client\olab\devel\repos\OLab4\OLab4-api\Service\bin\Debug\netcoreapp3.1'.
Using working directory 'd:\Client\olab\devel\repos\OLab4\OLab4-api\Service'.
Using root namespace 'OLabWebAPI'.
Using project directory 'd:\Client\olab\devel\repos\OLab4\OLab4-api\Service\'.
Remaining arguments: .
Finding design-time services for provider 'Pomelo.EntityFrameworkCore.MySql'...
Using design-time services from provider 'Pomelo.EntityFrameworkCore.MySql'.
Finding design-time services referenced by assembly 'OLabWebAPI'.
No referenced design-time services were found.
Finding IDesignTimeServices implementations in assembly 'OLabWebAPI'...
No design-time services were found.
System.InvalidOperationException: Sequence contains no matching element
   at System.Linq.ThrowHelper.ThrowNoMatchException()
   at System.Linq.Enumerable.Single[TSource](IEnumerable`1 source, Func`2 predicate)
   at Pomelo.EntityFrameworkCore.MySql.Scaffolding.Internal.MySqlDatabaseModelFactory.GetConstraints(DbConnection connection, IReadOnlyList`1 tables)
   at Pomelo.EntityFrameworkCore.MySql.Scaffolding.Internal.MySqlDatabaseModelFactory.GetTables(DbConnection connection, Func`3 filter)
   at Pomelo.EntityFrameworkCore.MySql.Scaffolding.Internal.MySqlDatabaseModelFactory.Create(DbConnection connection, DatabaseModelFactoryOptions options)
   at Pomelo.EntityFrameworkCore.MySql.Scaffolding.Internal.MySqlDatabaseModelFactory.Create(String connectionString, DatabaseModelFactoryOptions options)
   at Microsoft.EntityFrameworkCore.Scaffolding.Internal.ReverseEngineerScaffolder.ScaffoldModel(String connectionString, DatabaseModelFactoryOptions databaseOptions, ModelReverseEngineerOptions modelOptions, ModelCodeGenerationOptions codeOptions)
   at Microsoft.EntityFrameworkCore.Design.Internal.DatabaseOperations.ScaffoldContext(String provider, String connectionString, String outputDir, String outputContextDir, String dbContextClassName, IEnumerable`1 schemas, IEnumerable`1 tables, Boolean useDataAnnotations, Boolean overwriteFiles, Boolean useDatabaseNames)
   at Microsoft.EntityFrameworkCore.Design.OperationExecutor.ScaffoldContextImpl(String provider, String connectionString, String outputDir, String outputDbContextDir, String dbContextClassName, IEnumerable`1 schemaFilters, IEnumerable`1 tableFilters, Boolean useDataAnnotations, Boolean overwriteFiles, Boolean useDatabaseNames)
   at Microsoft.EntityFrameworkCore.Design.OperationExecutor.ScaffoldContext.<>c__DisplayClass0_0.<.ctor>b__0()
   at Microsoft.EntityFrameworkCore.Design.OperationExecutor.OperationBase.<>c__DisplayClass3_0`1.<Execute>b__0()
   at Microsoft.EntityFrameworkCore.Design.OperationExecutor.OperationBase.Execute(Action action)
Sequence contains no matching element

Further technical details

MySQL version: 10.3.29 MariaDB Operating system: Windows 10 Pomelo.EntityFrameworkCore.MySql version: 3.2.7

Other details about my project setup:

Solution made up of main ‘Services’ project, with a dependancy to a ‘Data’ classlib project that contains the DBContext.

Ran scaffolding in main .EXE project source directory (OLabWebAPI.csproj). DBContext is in dependant project called ‘Data’. Tried running the scaffolding in Data.csproj directory and same result.

I tried adding the following to the project that has my DBContext, to no avail:

using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Design;

// this is only used for scaffolding
public class DesignTimeOLabDBContext  : IDesignTimeDbContextFactory<OLabDBContext>
{
  public OLabDBContext CreateDbContext(string[] args)
  {
    var optionsBuilder = new DbContextOptionsBuilder<OLabDBContext>();
    // pass your design time connection string here
    optionsBuilder.UseMySql("connect string");
    return new OLabDBContext(optionsBuilder.Options);
  }
}

[lauxjpn]

@RotateAt60MPH The No design-time services were found. message is just an informational message that your project did not explicitly define any design-time services. Getting this message with the --verbose flag is normal, as most projects do not explicitly implement their own design-time services. So the message is completely unrelated to your issue.

---

However, to easily debug the issue (or even implement a workaround later), you can actually just add a custom design time service. Add the CustomMySqlDesignTimeServices and CustomMySqlDatabaseModelFactory classes from the following code to your project:

Program.cs

using System;
using System.Collections.Generic;
using System.Data.Common;
using System.Diagnostics;
using System.Linq;
using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Design;
using Microsoft.EntityFrameworkCore.Diagnostics;
using Microsoft.EntityFrameworkCore.Scaffolding;
using Microsoft.EntityFrameworkCore.Scaffolding.Metadata;
using Microsoft.EntityFrameworkCore.Storage;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Logging;
using Pomelo.EntityFrameworkCore.MySql.Design.Internal;
using Pomelo.EntityFrameworkCore.MySql.Infrastructure.Internal;
using Pomelo.EntityFrameworkCore.MySql.Scaffolding.Internal;

namespace IssueConsoleTemplate
{
    public class CustomMySqlDesignTimeServices : IDesignTimeServices
    {
        private readonly MySqlDesignTimeServices _originalMySqlDesignTimeServices;

        public CustomMySqlDesignTimeServices()
        {
            _originalMySqlDesignTimeServices = new MySqlDesignTimeServices();
        }

        public virtual void ConfigureDesignTimeServices(IServiceCollection serviceCollection)
        {
            _originalMySqlDesignTimeServices.ConfigureDesignTimeServices(serviceCollection);

            serviceCollection.AddScoped<IDatabaseModelFactory, CustomMySqlDatabaseModelFactory>();
        }
    }

    public class CustomMySqlDatabaseModelFactory : MySqlDatabaseModelFactory
    {
        private readonly IDiagnosticsLogger<DbLoggerCategory.Scaffolding> _logger;
        
        public CustomMySqlDatabaseModelFactory(
            IDiagnosticsLogger<DbLoggerCategory.Scaffolding> logger,
            IRelationalTypeMappingSource typeMappingSource,
            IMySqlOptions options)
            : base(
                logger,
                typeMappingSource,
                options)
        {
            _logger = logger;
        }
        
        private const string GetConstraintsQuery = @"SELECT
 	`CONSTRAINT_NAME`,
 	`TABLE_NAME`,
 	`REFERENCED_TABLE_NAME`,
 	GROUP_CONCAT(CONCAT_WS('|', `COLUMN_NAME`, `REFERENCED_COLUMN_NAME`) ORDER BY `ORDINAL_POSITION` SEPARATOR ',') AS PAIRED_COLUMNS,
 	(SELECT `DELETE_RULE` FROM `INFORMATION_SCHEMA`.`REFERENTIAL_CONSTRAINTS` WHERE `REFERENTIAL_CONSTRAINTS`.`CONSTRAINT_NAME` = `KEY_COLUMN_USAGE`.`CONSTRAINT_NAME` AND `REFERENTIAL_CONSTRAINTS`.`CONSTRAINT_SCHEMA` = `KEY_COLUMN_USAGE`.`CONSTRAINT_SCHEMA`) AS `DELETE_RULE`
 FROM `INFORMATION_SCHEMA`.`KEY_COLUMN_USAGE`
 WHERE `TABLE_SCHEMA` = '{0}'
 		AND `TABLE_NAME` = '{1}'
 		AND `CONSTRAINT_NAME` <> 'PRIMARY'
        AND `REFERENCED_TABLE_NAME` IS NOT NULL
        GROUP BY `CONSTRAINT_SCHEMA`,
        `CONSTRAINT_NAME`,
        `TABLE_NAME`,
        `REFERENCED_TABLE_NAME`;";

        protected virtual void GetConstraints(
            DbConnection connection,
            IReadOnlyList<DatabaseTable> tables)
        {
            Debugger.Launch(); // <-- launch the debugger

            foreach (var table in tables)
            {
                using (var command = connection.CreateCommand())
                {
                    command.CommandText = string.Format(GetConstraintsQuery, connection.Database, table.Name);
                    using (var reader = command.ExecuteReader())
                    {
                        while (reader.Read())
                        {
                            var referencedTableName = reader.GetString(2);
                            var referencedTable = tables.FirstOrDefault(t => t.Name == referencedTableName);
                            if (referencedTable == null)
                            {
                                // On operation systems with insensitive file name handling, the saved reference table name might have a
                                // different casing than the actual table name. (#1017)
                                // In the unlikely event that there are multiple tables with the same spelling, differing only in casing,
                                // we can't be certain which is the right match, so rather fail to be safe.
                                referencedTable = tables.Single(t => string.Equals(t.Name, referencedTableName, StringComparison.OrdinalIgnoreCase));
                            }
                            if (referencedTable != null)
                            {
                                var fkInfo = new DatabaseForeignKey {Name = reader.GetString(0), OnDelete = ConvertToReferentialAction(reader.GetString(4)), Table = table, PrincipalTable = referencedTable};
                                foreach (var pair in reader.GetString(3).Split(','))
                                {
                                    fkInfo.Columns.Add(table.Columns.Single(y =>
                                        string.Equals(y.Name, pair.Split('|')[0], StringComparison.OrdinalIgnoreCase)));
                                    fkInfo.PrincipalColumns.Add(fkInfo.PrincipalTable.Columns.Single(y =>
                                        string.Equals(y.Name, pair.Split('|')[1], StringComparison.OrdinalIgnoreCase)));
                                }

                                table.ForeignKeys.Add(fkInfo);
                            }
                            else
                            {
                                _logger.Logger.LogWarning($"Referenced table `{referencedTableName}` is not in dictionary.");
                            }
                        }
                    }
                }
            }
        }
    }

    internal static class Program
    {
        private static void Main()
        {
        }
    }
}

The CustomMySqlDatabaseModelFactory.GetConstraints() method is the one that the original 3.2.7 implementation uses (with the Debugger.Launch(); line added).

Just scaffold again and the JIT debugger should pop up. You can then just debug the method (or replace tables.Single() with tables.SingleOrDefault()).

[mguinness]

Probably related to PR https://github.com/PomeloFoundation/Pomelo.EntityFrameworkCore.MySql/pull/1364 that hasn’t been backported to 3.2-maint branch yet.