masums / efcoreautomigrator

Code driven auto-migrations for Entity Framework Core

EFCoreAutoMigrator

Code driven auto-migrations for Entity Framework Core

If you are using Entity Framework Core (EFCore) and want to auto-migrate your database you might know that this is a bit challenging (as noted in this thread dotnet/efcore#6214). This library builds upon suggested comments from the above thread as to how to implement this. Notes:

• This library was created as part of a bigger project to meet our particular need. Extensive testing and optimization has not been done on it. Please use this library with caution.
• This libray does not run manually created migration scripts for you (created via dotnet ef migrations add ...). For those you will still need to run dotnet ef database update. You can then switch over to migrating through EFCoreAutoMigrator once you run those migrations.

Getting Started

1. Installation

You can either clone this project and add it to your project directly or install it via nuget (See https://www.nuget.org/packages/CentridNet.EFCoreAutoMigrator)

2. Integrating

Once you have installed the package you can intergrate it by passing in your DbContext to the EFCoreAutoMigrator class (along with a logger). From there you can call PrepareMigration() which returns an instance of MigrationScriptExecutor. This instance is what you use to get the migration script to be executed (using GetMigrationScript()) and to execute it when ready (using MigrateDB()).

Below is a simple example of this based on the EFCore getting started tutorial found at https://docs.microsoft.com/en-us/ef/core/get-started

    using System;
    using System.IO;
    using System.Threading.Tasks;
    using CentridNet.EFCoreAutoMigrator;
    using Microsoft.EntityFrameworkCore;

    namespace EFCoreAutoMigratorExample
    {
        class Program
        {
            static void Main()
            {
                using (var db = new BloggingContext())
                {
                    AutoMigrateMyDB(db).Wait();  
                }
            }

            public static async Task AutoMigrateMyDB(DbContext db){
                EFCoreAutoMigrator dbMigrator = new EFCoreAutoMigrator(db, new Logger());
                MigrationScriptExecutor migrationScriptExcutor = await dbMigrator.PrepareMigration();
                await migrationScriptExcutor.MigrateDB();
                Console.WriteLine("Migration Complete");
            }
        }
    }

Below is a more complex example that allows for a more user driven/conditional migration.

    using System;
    using System.IO;
    using System.Threading.Tasks;
    using CentridNet.EFCoreAutoMigrator;
    using Microsoft.EntityFrameworkCore;

    namespace EFCoreAutoMigratorExample
    {
        class Program
        {
            static void Main()
            {
                using (var db = new BloggingContext())
                {
                    AutoMigrateMyDB(db).Wait();  
                }
            }

            public static async Task AutoMigrateMyDB(DbContext db){
                EFCoreAutoMigrator dbMigrator = new EFCoreAutoMigrator(db, new Logger());
                MigrationScriptExecutor migrationScriptExcutor = await dbMigrator.PrepareMigration();

                // Checking if there are migrations
                if (migrationScriptExcutor.HasMigrations()){
                    Console.WriteLine("The program `Example` wants to run the following script on your database: ");
                    Console.WriteLine("------");

                    // Printing out the script to be run if they are
                    Console.WriteLine(migrationScriptExcutor.GetMigrationScript());
                    Console.WriteLine("------");

                    Console.WriteLine("Do you want (R)un it, (S)ave the script or (C)ancel. ?");
                    string userInput = Console.ReadLine();
                    if (userInput.Length == 0){
                        Console.WriteLine("No value entered. Exiting...");
                        Environment.Exit(0);
                    }
                    if (userInput[0] == 'R'){
                        // Migrating
                        MigrationResult result = await migrationScriptExcutor.MigrateDB();
                        if (result == MigrationResult.Migrated){
                            Console.WriteLine("Completed succesfully.");
                        }
                        else if (result == MigrationResult.Noop){
                            Console.WriteLine("Completed. There was nothing to migrate.");
                        }
                        else if (result == MigrationResult.ErrorMigrating){
                            Console.WriteLine("Error occurred whilst migrating.");
                        }
                    }
                    else if (userInput[0] == 'S'){
                        using (StreamWriter writer = new StreamWriter(Path.Join(Environment.CurrentDirectory,"ERCoreAutoMigratorGenetaedScript.sql"))) 
                        {  
                            writer.WriteLine(migrationScriptExcutor.GetMigrationScript());
                            Console.WriteLine("Migration script saved succefully.");
                        } 
                    }
                }
                else{
                    Console.WriteLine("Completed. There was nothing to migrate.");
                }
                
            }
        }
    }

EFCoreAutoMigrator Configuration

ShouldAllowDestructive

This is used to state whether desctructive migrations are allowed or not. If not, and exception will occur when you run the PrepareMigration() method. Default is false.

Usage example:

    ...
    EFCoreAutoMigrator dbMigrator = new EFCoreAutoMigrator(db, new Logger())
                                        .ShouldAllowDestructive(true);
    ...

SetSnapshotHistoryLimit

For every migration EFCoreAutoMigrator runs it saves a snapshot (and other corresponding metadata...See SetMigrationTableMetadataClass below). Use this method to limt the number of snapshot saved. Default is unlimited

Usage example:

    ...
    EFCoreAutoMigrator dbMigrator = new EFCoreAutoMigrator(db, new Logger())
                                        .SetSnapshotHistoryLimit(1);
    ...

SetMigrationTableMetadataClass

This method takes in a class that implements the IAutoMigratorTableMetatdata interface. This class is then used to set the metadata field in the auto-migration database table and add a comment to the top of the generated sql script. This is useful if you want to track additional information, for instance, your application version associated with the migration. A default class is used, if not set.

Usage example:

        class MyMigrationMetadata : IAutoMigratorTableMetatdata {
            public string GetDBMetadata()
            {
                return "MyAppVersion: 1.0.0";
            }

            public string GetGeneratedScriptMetatdata()
            {
                return $"This script was auto-generated by MyApp (Version 1.0.0)";
            }
        }
    ...
    EFCoreAutoMigrator dbMigrator = new EFCoreAutoMigrator(db, new Logger())
                                        .SetMigrationTableMetadataClass(new MyMigrationMetadata());
    ...

SetMigrationProviderFactory

EFCoreAutoMigrator selects the appropiate migration provider (see below) for your connected database using the MigrationProviderFactory. If you want to replace this, use this method to pass in a class that implements the IMigrationProviderFactory interface. This is useful if you know exactly what database you will be using and want to remove the overhead associated with figuring out the database when migrating.

Usage example:

    public class MyMigrationProviderFactory : IMigrationProviderFactory{
        public MigrationsProvider Build(DBMigratorProps dBMigratorProps, MigrationScriptExecutor migrationScriptExecutor){

            if (dBMigratorProps.dbContext.Database.IsNpgsql()){
                return new PostgresMigrations(dBMigratorProps, migrationScriptExecutor);
            }
            return null;
        }        
    }
    ...
    EFCoreAutoMigrator dbMigrator = new EFCoreAutoMigrator(db, new Logger())
                                        .SetMigrationProviderFactory(new MyMigrationProviderFactory());
    ...

Migration Providers

In the EFCoreAutoMigrator library, MigrationProviders are responsible for creating and interacting with the auto-migration tables for the various databases. EFCoreAutoMigrator comes with providers for Postgres, MSSQL, MySQL, and SQLLite baked in.

If you want to create your own provider class (i.e for a particular database) you can do this by creating a class that inherits the MigrationProvider class. An example of this is below (For method code examples, look at the MigrationProviders already written. See src/MigrationProviders/Providers):

class MSSQLMigrations : MigrationsProvider
    {
        //TODO use CosmoDB
        public MSSQLMigrations(DBMigratorProps dbMigratorProps, MigrationScriptExecutor migrationScriptExecutor) : base(dbMigratorProps, migrationScriptExecutor){}

        protected override void EnsureMigrateTablesExist(){...};

        protected override void EnsureSnapshotLimitNotReached(){...};

        protected override AutoMigratorTable GetLastMigrationRecord(){...};

        protected override void UpdateMigrationTables(byte[] snapshotData){...};
    }

Once you have created a MigrationProvider you will need to let EFCoreAutoMigrator know it exists. You can either do this by creating your own MigrationProviderFactory (as described above) or write a DBContext extension method with the format [ProviderName]DBMigrations for the method name. Using the example above this will be:

public static MigrationsProvider CosmoDBDBMigrations(this DbContext dbContext, DBMigratorProps dbMigratorProps, MigrationScriptExecutor migrationScriptExecutor){   
            return new CosmoDBMigrations(dbMigratorProps, migrationScriptExecutor);
        }

Known Issues

• There is currently a migration issue that occurs when you change the namespace(s) associated with your DBSets (Error messasge Failed to compile previous snapshot). Will look into this and should provide a fix soon.

---

Contributing

EFCoreAutoMigrator is an opensource project and contributions are valued. If there is a bug fix please create a pull request explain what the bug is, how you fixed and tested it.

If it's a new feature, please add it as a issue with the label enhancement, detailing the new feature and why you think it's needed. Will discuss it there and once it's agreed upon you can create a pull request with the details highlighted above.

Authors

• Chido Warambwa - Initial Work - [email protected]

License

This project is licensed under the MIT License - see the LICENSE file for details

Thanks

Thanks to all those that have been contributing to the dicussion on this (see (https://github.com/dotnet/efcore/issues/6214)) and in particular, a huge thanks Jeremy Lakeman's code snippets that became the starting of point of this libray.