How can dbcontext support the migration of different databases in efcore advanced SaaS system

Preface

With the continuous development and iteration of the system, the default efcore Very powerful , But as the Saas Introduction of system efcore The multi tenancy pattern based on table fields is perfect , But multi tenancy based on database can also be used , But there are also disadvantages , The disadvantage is that there is no way to support different databases ,migration support multi database provider with single dbcontext, I am not talented , I inquired about , Official documents only state dbcontext How to realize the migration of multiple data sources , But lack is not a single dbcontext, This is a headache . So I wrote this blog with the principle of trying , Because I only have mmsql and mysql So this time we will use these two databases for testing

Advertising time

I have developed a efcore Separate table, database, read and write components

https://github.com/dotnetcore/sharding-core

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So don't talk more nonsense, let's start right away migration support multi database provider with single dbcontext

New projects

1. By the way, it depends on

2. Create a new one User class

[Table(nameof(User))]
public class User{
    public string UserId { get; set; }
    public string UserName { get; set; }
}

3. establish DbContext

public class MyDbContext:DbContext
{
    public DbSet<User> Users { get; set; }
    public MyDbContext(DbContextOptions<MyDbContext> options):base(options)
    {
        
    }

4.StartUp To configure

var provider = builder.Configuration.GetValue("Provider", "UnKnown");//Add-Migration InitialCreate -Context MyDbContext -OutputDir Migrations\SqlServer -Args "--provider SqlServer"//Add-Migration InitialCreate -Context MyDbContext -OutputDir Migrations\MySql -Args "--provider MySql"builder.Services.AddDbContext<MyDbContext>(options =>
{
    _ = provider switch
    {        "MySql" => options.UseMySql("server=127.0.0.1;port=3306;database=DBMultiDataBase;userid=root;password=L6yBtV6qNENrwBy7;", new MySqlServerVersion(new Version())),        "SqlServer" => options.UseSqlServer("Data Source=localhost;Initial Catalog=DBMultiDataBase;Integrated Security=True;"),
        _ => throw new Exception($"Unsupported provider: {provider}")
    };
});

Migrate differentiated databases

Create a new migration namespace provider

public interface IMigrationNamespace
    {        string GetNamespace();
    }

mysql and sqlserver The implementation of is project name migration folder

public class MySqlMigrationNamespace:IMigrationNamespace
    {
        public string GetNamespace()
        {            return "EFCoreMigrateMultiDatabase.Migrations.MySql";
        }
    }

    public class SqlServerMigrationNamespace:IMigrationNamespace
    {
        public string GetNamespace()
        {            return "EFCoreMigrateMultiDatabase.Migrations.SqlServer";
        }
    }

efcore Expand

add to efcore Expand

public class MigrationNamespaceExtension : IDbContextOptionsExtension
    {
        public IMigrationNamespace MigrationNamespace { get; }

        public MigrationNamespaceExtension(IMigrationNamespace migrationNamespace)
        {
            MigrationNamespace = migrationNamespace;
        }
        public void ApplyServices(IServiceCollection services)
        {
            services.AddSingleton<IMigrationNamespace>(sp => MigrationNamespace);
        }

        public void Validate(IDbContextOptions options)
        {
        }


        public DbContextOptionsExtensionInfo Info => new MigrationNamespaceExtensionInfo(this);

        private class MigrationNamespaceExtensionInfo : DbContextOptionsExtensionInfo
        {
            private readonly MigrationNamespaceExtension _migrationNamespaceExtension;
            public MigrationNamespaceExtensionInfo(IDbContextOptionsExtension extension) : base(extension)
            {
                _migrationNamespaceExtension = (MigrationNamespaceExtension)extension;
            }

            public override int GetServiceProviderHashCode() => _migrationNamespaceExtension.MigrationNamespace.GetNamespace().GetHashCode();

            public override bool ShouldUseSameServiceProvider(DbContextOptionsExtensionInfo other) => true;

            public override void PopulateDebugInfo(IDictionary<string, string> debugInfo)
            {
            }

            public override bool IsDatabaseProvider => false;
            public override string LogFragment => "MigrationNamespaceExtension";
        }
    }

rewrite MigrationsAssembly Support multiple databases

public class EFCoreMultiDatabaseMigrationsAssembly: IMigrationsAssembly
    {
        public  string MigrationNamespace { get; }
        private readonly IMigrationsIdGenerator _idGenerator;
        private readonly IDiagnosticsLogger<DbLoggerCategory.Migrations> _logger;
        private IReadOnlyDictionary<string, TypeInfo>? _migrations;
        private ModelSnapshot? _modelSnapshot;
        private readonly Type _contextType;        /// <summary>
        ///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to
        ///     the same compatibility standards as public APIs. It may be changed or removed without notice in
        ///     any release. You should only use it directly in your code with extreme caution and knowing that
        ///     doing so can result in application failures when updating to a new Entity Framework Core release.
        /// </summary>
        public EFCoreMultiDatabaseMigrationsAssembly(
            IMigrationNamespace migrationNamespace,
            ICurrentDbContext currentContext,
            IDbContextOptions options,
            IMigrationsIdGenerator idGenerator,
            IDiagnosticsLogger<DbLoggerCategory.Migrations> logger)
        {

            _contextType = currentContext.Context.GetType();

            var assemblyName = RelationalOptionsExtension.Extract(options)?.MigrationsAssembly;
            Assembly = assemblyName == null
                ? _contextType.Assembly
                : Assembly.Load(new AssemblyName(assemblyName));

            MigrationNamespace = migrationNamespace.GetNamespace();
            _idGenerator = idGenerator;
            _logger = logger;
        }        /// <summary>
        ///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to
        ///     the same compatibility standards as public APIs. It may be changed or removed without notice in
        ///     any release. You should only use it directly in your code with extreme caution and knowing that
        ///     doing so can result in application failures when updating to a new Entity Framework Core release.
        /// </summary>
        public virtual IReadOnlyDictionary<string, TypeInfo> Migrations
        {
            get
            {
                IReadOnlyDictionary<string, TypeInfo> Create()
                {
                    var result = new SortedList<string, TypeInfo>();
                    var items
                        = from t in Assembly.GetConstructibleTypes()
                          where t.IsSubclassOf(typeof(Migration))&& print(t)
                                && t.Namespace.Equals(MigrationNamespace)
                              && t.GetCustomAttribute<DbContextAttribute>()?.ContextType == _contextType
                          let id = t.GetCustomAttribute<MigrationAttribute>()?.Id
                          orderby id
                          select (id, t);
                    Console.WriteLine("Migrations:" + items.Count());
                    foreach (var (id, t) in items)
                    {                        if (id == null)
                        {
                            _logger.MigrationAttributeMissingWarning(t);                            continue;
                        }

                        result.Add(id, t);
                    }                    return result;
                }                return _migrations ??= Create();
            }
        }

        private bool print(TypeInfo t)
        {
            Console.WriteLine(MigrationNamespace);
            Console.WriteLine(t.Namespace);            return true;
        }        /// <summary>
        ///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to
        ///     the same compatibility standards as public APIs. It may be changed or removed without notice in
        ///     any release. You should only use it directly in your code with extreme caution and knowing that
        ///     doing so can result in application failures when updating to a new Entity Framework Core release.
        /// </summary>
        public virtual ModelSnapshot? ModelSnapshot
            => GetMod();

        private ModelSnapshot GetMod()
        {
            Console.WriteLine("_modelSnapshot:"+ _modelSnapshot);            if (_modelSnapshot == null)
            {
                Console.WriteLine("_modelSnapshot:null");
                _modelSnapshot = (from t in Assembly.GetConstructibleTypes()
                        where t.IsSubclassOf(typeof(ModelSnapshot)) && print(t)
                                                                    && MigrationNamespace.Equals(t?.Namespace)
                                                                    && t.GetCustomAttribute<DbContextAttribute>()?.ContextType == _contextType
                        select (ModelSnapshot)Activator.CreateInstance(t.AsType())!)
                    .FirstOrDefault();

                Console.WriteLine("_modelSnapshot:" + _modelSnapshot);
            }            return _modelSnapshot;
        }        /// <summary>
        ///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to
        ///     the same compatibility standards as public APIs. It may be changed or removed without notice in
        ///     any release. You should only use it directly in your code with extreme caution and knowing that
        ///     doing so can result in application failures when updating to a new Entity Framework Core release.
        /// </summary>
        public virtual Assembly Assembly { get; }        /// <summary>
        ///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to
        ///     the same compatibility standards as public APIs. It may be changed or removed without notice in
        ///     any release. You should only use it directly in your code with extreme caution and knowing that
        ///     doing so can result in application failures when updating to a new Entity Framework Core release.
        /// </summary>
        public virtual string? FindMigrationId(string nameOrId)
            => Migrations.Keys
                .Where(
                    _idGenerator.IsValidId(nameOrId)                        // ReSharper disable once ImplicitlyCapturedClosure
                        ? id => string.Equals(id, nameOrId, StringComparison.OrdinalIgnoreCase)
                        : id => string.Equals(_idGenerator.GetName(id), nameOrId, StringComparison.OrdinalIgnoreCase))
                .FirstOrDefault();        /// <summary>
        ///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to
        ///     the same compatibility standards as public APIs. It may be changed or removed without notice in
        ///     any release. You should only use it directly in your code with extreme caution and knowing that
        ///     doing so can result in application failures when updating to a new Entity Framework Core release.
        /// </summary>
        public virtual Migration CreateMigration(TypeInfo migrationClass, string activeProvider)
        {
            Console.WriteLine(migrationClass.FullName);

            var migration = (Migration)Activator.CreateInstance(migrationClass.AsType())!;
            migration.ActiveProvider = activeProvider;            return migration;
        }
    } Fold 

To write startup

Reference resources  https://docs.microsoft.com/en-us/ef/core/managing-schemas/migrations/providers?tabs=vs

//Add-Migration InitialCreate -Context MyDbContext -OutputDir Migrations\SqlServer -Args "--provider SqlServer"//Add-Migration InitialCreate -Context MyDbContext -OutputDir Migrations\MySql -Args "--provider MySql"//update-database -Args "--provider MySql"//update-database -Args "--provider SqlServer"builder.Services.AddDbContext<MyDbContext>(options =>
{
    options.ReplaceService<IMigrationsAssembly, EFCoreMultiDatabaseMigrationsAssembly>();
    _ = provider switch
    {        "MySql" => options.UseMySql("server=127.0.0.1;port=3306;database=DBMultiDataBase;userid=root;password=L6yBtV6qNENrwBy7;", new MySqlServerVersion(new Version()))
            .UseMigrationNamespace(new MySqlMigrationNamespace()),        "SqlServer" => options.UseSqlServer("Data Source=localhost;Initial Catalog=DBMultiDataBase;Integrated Security=True;")
        .UseMigrationNamespace(new SqlServerMigrationNamespace()),
        _ => throw new Exception($"Unsupported provider: {provider}")
    };
});

So far, I think we should have achieved , But if we execute two migration commands separately, the previous one will be overwritten , After a whole afternoon debug The final finding of debugging is that when the migration script generates and writes files, it will judge the current DbContext' Of ModelSnapshot, The same dbcontext The generated files are the same , So we have two choices

• 1. Make the generated file names different

• 2. Give Way ModelSnapshot Do not perform deep query, and only process in the current directory
  Here we choose the second

public class MyMigrationsScaffolder: MigrationsScaffolder
    {
        private readonly Type _contextType;
        public MyMigrationsScaffolder(MigrationsScaffolderDependencies dependencies) : base(dependencies)
        {
            _contextType = dependencies.CurrentContext.Context.GetType();
        }
        protected override string GetDirectory(string projectDir, string? siblingFileName, string subnamespace)
        {
            var defaultDirectory = Path.Combine(projectDir, Path.Combine(subnamespace.Split('.')));            if (siblingFileName != null)
            {                if (!siblingFileName.StartsWith(_contextType.Name + "ModelSnapshot."))
                {
                    var siblingPath = TryGetProjectFile(projectDir, siblingFileName);                    if (siblingPath != null)
                    {
                        var lastDirectory = Path.GetDirectoryName(siblingPath)!;                        if (!defaultDirectory.Equals(lastDirectory, StringComparison.OrdinalIgnoreCase))
                        {
                            Dependencies.OperationReporter.WriteVerbose(DesignStrings.ReusingNamespace(siblingFileName));                            return lastDirectory;
                        }
                    }
                }
            }            return defaultDirectory;
        }
    }

add to designservices

public class MyMigrationDesignTimeServices: IDesignTimeServices
    {
        public void ConfigureDesignTimeServices(IServiceCollection serviceCollection)
        {
            serviceCollection.AddSingleton<IMigrationsScaffolder, MyMigrationsScaffolder>();
        }
    }

transfer

Run two migration commands respectively

Run the update database command

Remember that we need to add options to the parameters

Next up

Next time we will realize efcore stay Saas Under the system multi-tenancy +code-first( transfer )+ table + sub-treasury + Read / write separation + Dynamic sub table + Dynamic sub Library + Dynamic read write separation + Dynamically add multi tenancy The whole process is zero sql Script Solutions for

Is it right? buffer Full stack

Last, last

Enclosed demo:EFCoreMigrateMultiDatabase https://github.com/xuejmnet/EFCoreMigrateMultiDatabase

You've seen it here. Are you sure you don't want to order star Or like it , a .Net Have to learn the sub database and sub table solution , It is simply understood as sharding-jdbc stay .net And support more features and better data aggregation , With native performance 97%, And no business intrusion , Support all non segmented efcore Native query

• github Address  https://github.com/xuejmnet/sharding-core

• gitee Address  https://gitee.com/dotnetchina/sharding-core