DatabaseContext.cs

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using System;
using System.Globalization;
using System.Linq;
using System.Reflection;
using System.Threading;
using System.Threading.Tasks;
 
using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Infrastructure;
using Microsoft.EntityFrameworkCore.Migrations;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Logging;
 
using Tgstation.Server.Host.Configuration;
using Tgstation.Server.Host.Database.Migrations;
using Tgstation.Server.Host.Models;
 
namespace Tgstation.Server.Host.Database
{
#pragma warning disable CA1506 // TODO: Decomplexify
    public abstract class DatabaseContext : DbContext, IDatabaseContext
    {
        public DbSet<User> Users { get; set; }
 
        public DbSet<Instance> Instances { get; set; }
 
        public DbSet<CompileJob> CompileJobs { get; set; }
 
        public DbSet<RevisionInformation> RevisionInformations { get; set; }
 
        public DbSet<DreamMakerSettings> DreamMakerSettings { get; set; }
 
        public DbSet<ChatBot> ChatBots { get; set; }
 
        public DbSet<DreamDaemonSettings> DreamDaemonSettings { get; set; }
 
        public DbSet<RepositorySettings> RepositorySettings { get; set; }
 
        public DbSet<InstancePermissionSet> InstancePermissionSets { get; set; }
 
        public DbSet<ChatChannel> ChatChannels { get; set; }
 
        public DbSet<Job> Jobs { get; set; }
 
        public DbSet<ReattachInformation> ReattachInformations { get; set; }
 
        public DbSet<TestMerge> TestMerges { get; set; }
 
        public DbSet<RevInfoTestMerge> RevInfoTestMerges { get; set; }
 
        public DbSet<OAuthConnection> OAuthConnections { get; set; }
 
        public DbSet<OidcConnection> OidcConnections { get; set; }
 
        public DbSet<PermissionSet> PermissionSets { get; set; }
 
        public DbSet<UserGroup> Groups { get; set; }
 
        IDatabaseCollection<User> IDatabaseContext.Users => usersCollection;
 
        IDatabaseCollection<Instance> IDatabaseContext.Instances => instancesCollection;
 
        IDatabaseCollection<InstancePermissionSet> IDatabaseContext.InstancePermissionSets => instancePermissionSetsCollection;
 
        IDatabaseCollection<Job> IDatabaseContext.Jobs => jobsCollection;
 
        IDatabaseCollection<CompileJob> IDatabaseContext.CompileJobs => compileJobsCollection;
 
        IDatabaseCollection<RevisionInformation> IDatabaseContext.RevisionInformations => revisionInformationsCollection;
 
        IDatabaseCollection<RevInfoTestMerge> IDatabaseContext.RevInfoTestMerges => revInfoTestMergesCollection;
 
        IDatabaseCollection<TestMerge> IDatabaseContext.TestMerges => testMergesCollection;
 
        IDatabaseCollection<DreamMakerSettings> IDatabaseContext.DreamMakerSettings => dreamMakerSettingsCollection;
 
        IDatabaseCollection<DreamDaemonSettings> IDatabaseContext.DreamDaemonSettings => dreamDaemonSettingsCollection;
 
        IDatabaseCollection<ChatBot> IDatabaseContext.ChatBots => chatBotsCollection;
 
        IDatabaseCollection<ChatChannel> IDatabaseContext.ChatChannels => chatChannelsCollection;
 
        IDatabaseCollection<RepositorySettings> IDatabaseContext.RepositorySettings => repositorySettingsCollection;
 
        IDatabaseCollection<ReattachInformation> IDatabaseContext.ReattachInformations => reattachInformationsCollection;
 
        IDatabaseCollection<OAuthConnection> IDatabaseContext.OAuthConnections => oAuthConnections;
 
        IDatabaseCollection<OidcConnection> IDatabaseContext.OidcConnections => oidcConnections;
 
        IDatabaseCollection<UserGroup> IDatabaseContext.Groups => groups;
 
        IDatabaseCollection<PermissionSet> IDatabaseContext.PermissionSets => permissionSets;
 
        protected virtual DeleteBehavior RevInfoCompileJobDeleteBehavior => DeleteBehavior.ClientNoAction;
 
        readonly IDatabaseCollection<User> usersCollection;
 
        readonly IDatabaseCollection<Instance> instancesCollection;
 
        readonly IDatabaseCollection<CompileJob> compileJobsCollection;
 
        readonly IDatabaseCollection<InstancePermissionSet> instancePermissionSetsCollection;
 
        readonly IDatabaseCollection<Job> jobsCollection;
 
        readonly IDatabaseCollection<RevisionInformation> revisionInformationsCollection;
 
        readonly IDatabaseCollection<RevInfoTestMerge> revInfoTestMergesCollection;
 
        readonly IDatabaseCollection<TestMerge> testMergesCollection;
 
        readonly IDatabaseCollection<DreamMakerSettings> dreamMakerSettingsCollection;
 
        readonly IDatabaseCollection<DreamDaemonSettings> dreamDaemonSettingsCollection;
 
        readonly IDatabaseCollection<ChatBot> chatBotsCollection;
 
        readonly IDatabaseCollection<ChatChannel> chatChannelsCollection;
 
        readonly IDatabaseCollection<RepositorySettings> repositorySettingsCollection;
 
        readonly IDatabaseCollection<ReattachInformation> reattachInformationsCollection;
 
        readonly IDatabaseCollection<OAuthConnection> oAuthConnections;
 
        readonly IDatabaseCollection<OidcConnection> oidcConnections;
 
        readonly IDatabaseCollection<UserGroup> groups;
 
        readonly IDatabaseCollection<PermissionSet> permissionSets;
 
        public static Action<DbContextOptionsBuilder, DatabaseConfiguration> GetConfigureAction<TDatabaseContext>()
            where TDatabaseContext : DatabaseContext
        {
            // HACK HACK HACK HACK HACK
            const string ConfigureMethodName = nameof(SqlServerDatabaseContext.ConfigureWith);
            var configureFunction = typeof(TDatabaseContext).GetMethod(
                ConfigureMethodName,
                BindingFlags.Public | BindingFlags.Static)
                ?? throw new InvalidOperationException($"Context type {typeof(TDatabaseContext).FullName} missing static {ConfigureMethodName} function!");
            return (optionsBuilder, config) => configureFunction.Invoke(null, [optionsBuilder, config]);
        }
 
        protected DatabaseContext(DbContextOptions dbContextOptions)
            : base(dbContextOptions)
        {
            usersCollection = new DatabaseCollection<User>(Users!);
            instancesCollection = new DatabaseCollection<Instance>(Instances!);
            instancePermissionSetsCollection = new DatabaseCollection<InstancePermissionSet>(InstancePermissionSets!);
            compileJobsCollection = new DatabaseCollection<CompileJob>(CompileJobs!);
            repositorySettingsCollection = new DatabaseCollection<RepositorySettings>(RepositorySettings!);
            dreamMakerSettingsCollection = new DatabaseCollection<DreamMakerSettings>(DreamMakerSettings!);
            dreamDaemonSettingsCollection = new DatabaseCollection<DreamDaemonSettings>(DreamDaemonSettings!);
            chatBotsCollection = new DatabaseCollection<ChatBot>(ChatBots!);
            chatChannelsCollection = new DatabaseCollection<ChatChannel>(ChatChannels!);
            revisionInformationsCollection = new DatabaseCollection<RevisionInformation>(RevisionInformations!);
            revInfoTestMergesCollection = new DatabaseCollection<RevInfoTestMerge>(RevInfoTestMerges!);
            testMergesCollection = new DatabaseCollection<TestMerge>(TestMerges!);
            jobsCollection = new DatabaseCollection<Job>(Jobs!);
            reattachInformationsCollection = new DatabaseCollection<ReattachInformation>(ReattachInformations!);
            oAuthConnections = new DatabaseCollection<OAuthConnection>(OAuthConnections!);
            oidcConnections = new DatabaseCollection<OidcConnection>(OidcConnections!);
            groups = new DatabaseCollection<UserGroup>(Groups!);
            permissionSets = new DatabaseCollection<PermissionSet>(PermissionSets!);
        }
 
        public Task Save(CancellationToken cancellationToken) => SaveChangesAsync(cancellationToken);
 
        public Task Drop(CancellationToken cancellationToken) => Database.EnsureDeletedAsync(cancellationToken);
 
        public async ValueTask<bool> Migrate(ILogger<DatabaseContext> logger, CancellationToken cancellationToken)
        {
            ArgumentNullException.ThrowIfNull(logger);
            var migrations = await Database.GetAppliedMigrationsAsync(cancellationToken);
            var wasEmpty = !migrations.Any();
 
            if (wasEmpty || (await Database.GetPendingMigrationsAsync(cancellationToken)).Any())
            {
                logger.LogInformation("Migrating database...");
                await Database.MigrateAsync(cancellationToken);
            }
            else
                logger.LogDebug("No migrations to apply");
 
            wasEmpty |= !await Users.AsQueryable().AnyAsync(cancellationToken);
 
            return wasEmpty;
        }
 
        public async ValueTask SchemaDowngradeForServerVersion(
            ILogger<DatabaseContext> logger,
            Version targetVersion,
            DatabaseType currentDatabaseType,
            CancellationToken cancellationToken)
        {
            ArgumentNullException.ThrowIfNull(logger);
            ArgumentNullException.ThrowIfNull(targetVersion);
            if (targetVersion < new Version(4, 0))
                throw new ArgumentOutOfRangeException(nameof(targetVersion), targetVersion, "Cannot migrate below version 4.0.0!");
 
            if (currentDatabaseType == DatabaseType.PostgresSql && targetVersion < new Version(4, 3, 0))
                throw new NotSupportedException("Cannot migrate below version 4.3.0 with PostgresSql!");
 
            if (currentDatabaseType == DatabaseType.MariaDB)
                currentDatabaseType = DatabaseType.MySql; // Keeping switch expressions while avoiding `or` syntax from C#9
 
            if (targetVersion < new Version(4, 1, 0))
                throw new NotSupportedException("Cannot migrate below version 4.1.0!");
 
            var targetMigration = GetTargetMigration(targetVersion, currentDatabaseType);
 
            if (targetMigration == null)
            {
                logger.LogDebug("No down migration required.");
                return;
            }
 
            // already setup
            var migrationSubstitution = currentDatabaseType switch
            {
                DatabaseType.SqlServer => null, // already setup
                DatabaseType.MySql => "MY{0}",
                DatabaseType.Sqlite => "SL{0}",
                DatabaseType.PostgresSql => "PG{0}",
                _ => throw new InvalidOperationException($"Invalid DatabaseType: {currentDatabaseType}"),
            };
 
            if (migrationSubstitution != null)
                targetMigration = String.Format(CultureInfo.InvariantCulture, migrationSubstitution, targetMigration[2..]);
 
            // even though it clearly implements it in the DatabaseFacade definition this won't work without casting (╯ಠ益ಠ)╯︵ ┻━┻
            var dbServiceProvider = ((IInfrastructure<IServiceProvider>)Database).Instance;
            var migrator = dbServiceProvider.GetRequiredService<IMigrator>();
 
            logger.LogInformation("Migrating down to version {targetVersion}. Target: {targetMigration}", targetVersion, targetMigration);
            try
            {
                await migrator.MigrateAsync(targetMigration, cancellationToken);
            }
            catch (Exception e)
            {
                logger.LogCritical(e, "Failed to migrate!");
            }
        }
 
        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            ArgumentNullException.ThrowIfNull(modelBuilder);
 
            base.OnModelCreating(modelBuilder);
 
            var userModel = modelBuilder.Entity<User>();
            userModel.HasIndex(x => x.CanonicalName).IsUnique();
            userModel.HasIndex(x => x.SystemIdentifier).IsUnique();
            userModel.HasMany(x => x.TestMerges).WithOne(x => x.MergedBy).OnDelete(DeleteBehavior.Restrict);
            userModel.HasMany(x => x.OAuthConnections).WithOne(x => x.User).OnDelete(DeleteBehavior.Cascade);
            userModel.HasMany(x => x.OidcConnections).WithOne(x => x.User).OnDelete(DeleteBehavior.Cascade);
 
            modelBuilder.Entity<OAuthConnection>().HasIndex(x => new { x.Provider, x.ExternalUserId }).IsUnique();
            modelBuilder.Entity<OidcConnection>().HasIndex(x => new { x.SchemeKey, x.ExternalUserId }).IsUnique();
 
            var groupsModel = modelBuilder.Entity<UserGroup>();
            groupsModel.HasIndex(x => x.Name).IsUnique();
            groupsModel.HasMany(x => x.Users).WithOne(x => x.Group).OnDelete(DeleteBehavior.ClientSetNull);
 
            var permissionSetModel = modelBuilder.Entity<PermissionSet>();
            permissionSetModel.HasOne(x => x.Group).WithOne(x => x.PermissionSet).OnDelete(DeleteBehavior.Cascade);
            permissionSetModel.HasOne(x => x.User).WithOne(x => x.PermissionSet).OnDelete(DeleteBehavior.Cascade);
            permissionSetModel.HasMany(x => x.InstancePermissionSets).WithOne(x => x.PermissionSet).OnDelete(DeleteBehavior.Cascade);
 
            modelBuilder.Entity<InstancePermissionSet>().HasIndex(x => new { x.PermissionSetId, x.InstanceId }).IsUnique();
 
            var revInfo = modelBuilder.Entity<RevisionInformation>();
            revInfo.HasMany(x => x.ActiveTestMerges).WithOne(x => x.RevisionInformation).OnDelete(DeleteBehavior.Cascade);
            revInfo.HasOne(x => x.PrimaryTestMerge).WithOne(x => x.PrimaryRevisionInformation).OnDelete(DeleteBehavior.Cascade);
            revInfo.HasIndex(x => new { x.InstanceId, x.CommitSha }).IsUnique();
 
            // IMPORTANT: When an instance is deleted (detached) it cascades into the maze of revinfo/testmerge/ritm/compilejob/job/ri relations
            // This maze starts at revInfo and jobs
            // jobs takes care of deleting compile jobs and ris
            // rev info takes care of the rest
            // Break the link here so the db doesn't shit itself complaining about cascading deletes
            // EF will handle making the right query to destroy everything
            // UPDATE: I fuck with this constantly in hopes of eliminating FK issues on instance detack
            revInfo.HasMany(x => x.CompileJobs).WithOne(x => x.RevisionInformation).OnDelete(RevInfoCompileJobDeleteBehavior);
 
            // Also break the link between ritm and testmerge so it doesn't cycle in a triangle with rev info
            modelBuilder.Entity<TestMerge>().HasMany(x => x.RevisonInformations).WithOne(x => x.TestMerge).OnDelete(DeleteBehavior.ClientNoAction);
 
            var compileJob = modelBuilder.Entity<CompileJob>();
            compileJob.HasIndex(x => x.DirectoryName);
            compileJob.HasOne(x => x.Job).WithOne().OnDelete(DeleteBehavior.Cascade);
 
            modelBuilder.Entity<ReattachInformation>().HasOne(x => x.CompileJob).WithMany().OnDelete(DeleteBehavior.Cascade);
 
            var chatChannel = modelBuilder.Entity<ChatChannel>();
            chatChannel.HasIndex(x => new { x.ChatSettingsId, x.IrcChannel }).IsUnique();
            chatChannel.HasIndex(x => new { x.ChatSettingsId, x.DiscordChannelId }).IsUnique();
            chatChannel.HasOne(x => x.ChatSettings).WithMany(x => x.Channels).HasForeignKey(x => x.ChatSettingsId).OnDelete(DeleteBehavior.Cascade);
 
            modelBuilder.Entity<ChatBot>().HasIndex(x => new { x.InstanceId, x.Name }).IsUnique();
 
            var instanceModel = modelBuilder.Entity<Instance>();
            instanceModel.HasIndex(x => new { x.Path, x.SwarmIdentifer }).IsUnique();
            instanceModel.HasMany(x => x.ChatSettings).WithOne(x => x.Instance).OnDelete(DeleteBehavior.Cascade);
            instanceModel.HasOne(x => x.DreamDaemonSettings).WithOne(x => x.Instance).OnDelete(DeleteBehavior.Cascade);
            instanceModel.HasOne(x => x.DreamMakerSettings).WithOne(x => x.Instance).OnDelete(DeleteBehavior.Cascade);
            instanceModel.HasOne(x => x.RepositorySettings).WithOne(x => x.Instance).OnDelete(DeleteBehavior.Cascade);
            instanceModel.HasMany(x => x.RevisionInformations).WithOne(x => x.Instance).OnDelete(DeleteBehavior.Cascade);
            instanceModel.HasMany(x => x.InstancePermissionSets).WithOne(x => x.Instance).OnDelete(DeleteBehavior.Cascade);
            instanceModel.HasMany(x => x.Jobs).WithOne(x => x.Instance).OnDelete(DeleteBehavior.Cascade);
        }
 
        // HEY YOU
        // IF YOU HAVE A TEST THAT'S CREATING ERRORS BECAUSE THESE VALUES AREN'T SET CORRECTLY THERE'S MORE TO FIXING IT THAN JUST UPDATING THEM
        // IN THE FUNCTION BELOW YOU ALSO NEED TO CORRECTLY SET THE RIGHT MIGRATION TO DOWNGRADE TO FOR THE LAST TGS VERSION
        // YOU ALSO NEED TO UPDATE THE SWARM PROTOCOL MAJOR VERSION
        // IF THIS BREAKS AGAIN I WILL PERSONALLY HAUNT YOUR ASS WHEN I DIE
 
        internal static readonly Type MSLatestMigration = typeof(MSAddOidcConnections);
 
        internal static readonly Type MYLatestMigration = typeof(MYAddOidcConnections);
 
        internal static readonly Type PGLatestMigration = typeof(PGAddOidcConnections);
 
        internal static readonly Type SLLatestMigration = typeof(SLAddOidcConnections);
 
        private string? GetTargetMigration(Version targetVersion, DatabaseType currentDatabaseType)
        {
            // Update this with new migrations as they are made
            string? targetMigration = null;
 
            string BadDatabaseType() => throw new ArgumentException($"Invalid DatabaseType: {currentDatabaseType}", nameof(currentDatabaseType));
 
            // !!! DON'T FORGET TO UPDATE THE SWARM PROTOCOL MAJOR VERSION !!!
            if (targetVersion < new Version(6, 15, 0))
                targetMigration = currentDatabaseType switch
                {
                    DatabaseType.MySql => nameof(MYAddAutoStartAndStop),
                    DatabaseType.PostgresSql => nameof(PGAddAutoStartAndStop),
                    DatabaseType.SqlServer => nameof(MSAddAutoStartAndStop),
                    DatabaseType.Sqlite => nameof(SLAddAutoStartAndStop),
                    _ => BadDatabaseType(),
                };
 
            if (targetVersion < new Version(6, 12, 0))
                targetMigration = currentDatabaseType switch
                {
                    DatabaseType.MySql => nameof(MYAddDMApiValidationMode),
                    DatabaseType.PostgresSql => nameof(PGAddDMApiValidationMode),
                    DatabaseType.SqlServer => nameof(MSAddDMApiValidationMode),
                    DatabaseType.Sqlite => nameof(SLAddDMApiValidationMode),
                    _ => BadDatabaseType(),
                };
 
            if (targetVersion < new Version(6, 7, 0))
                targetMigration = currentDatabaseType switch
                {
                    DatabaseType.MySql => nameof(MYAddCronAutoUpdates),
                    DatabaseType.PostgresSql => nameof(PGAddCronAutoUpdates),
                    DatabaseType.SqlServer => nameof(MSAddCronAutoUpdates),
                    DatabaseType.Sqlite => nameof(SLAddCronAutoUpdates),
                    _ => BadDatabaseType(),
                };
 
            if (targetVersion < new Version(6, 6, 0))
                targetMigration = currentDatabaseType switch
                {
                    DatabaseType.MySql => nameof(MYAddCompilerAdditionalArguments),
                    DatabaseType.PostgresSql => nameof(PGAddCompilerAdditionalArguments),
                    DatabaseType.SqlServer => nameof(MSAddCompilerAdditionalArguments),
                    DatabaseType.Sqlite => nameof(SLAddCompilerAdditionalArguments),
                    _ => BadDatabaseType(),
                };
 
            if (targetVersion < new Version(6, 5, 0))
                targetMigration = currentDatabaseType switch
                {
                    DatabaseType.MySql => nameof(MYAddMinidumpsOption),
                    DatabaseType.PostgresSql => nameof(PGAddMinidumpsOption),
                    DatabaseType.SqlServer => nameof(MSAddMinidumpsOption),
                    DatabaseType.Sqlite => nameof(SLAddMinidumpsOption),
                    _ => BadDatabaseType(),
                };
 
            if (targetVersion < new Version(6, 2, 0))
                targetMigration = currentDatabaseType switch
                {
                    DatabaseType.MySql => nameof(MYAddTopicPort),
                    DatabaseType.PostgresSql => nameof(PGAddTopicPort),
                    DatabaseType.SqlServer => nameof(MSAddTopicPort),
                    DatabaseType.Sqlite => nameof(SLAddTopicPort),
                    _ => BadDatabaseType(),
                };
 
            if (targetVersion < new Version(6, 0, 0))
                targetMigration = currentDatabaseType switch
                {
                    DatabaseType.MySql => nameof(MYAddJobCodes),
                    DatabaseType.PostgresSql => nameof(PGAddJobCodes),
                    DatabaseType.SqlServer => nameof(MSAddJobCodes),
                    DatabaseType.Sqlite => nameof(SLAddJobCodes),
                    _ => BadDatabaseType(),
                };
            if (targetVersion < new Version(5, 17, 0))
                targetMigration = currentDatabaseType switch
                {
                    DatabaseType.MySql => nameof(MYAddMapThreads),
                    DatabaseType.PostgresSql => nameof(PGAddMapThreads),
                    DatabaseType.SqlServer => nameof(MSAddMapThreads),
                    DatabaseType.Sqlite => nameof(SLAddMapThreads),
                    _ => BadDatabaseType(),
                };
            if (targetVersion < new Version(5, 13, 0))
                targetMigration = currentDatabaseType switch
                {
                    DatabaseType.MySql => nameof(MYAddReattachInfoInitialCompileJob),
                    DatabaseType.PostgresSql => nameof(PGAddReattachInfoInitialCompileJob),
                    DatabaseType.SqlServer => nameof(MSAddReattachInfoInitialCompileJob),
                    DatabaseType.Sqlite => nameof(SLAddReattachInfoInitialCompileJob),
                    _ => BadDatabaseType(),
                };
            if (targetVersion < new Version(5, 7, 3))
                targetMigration = currentDatabaseType switch
                {
                    DatabaseType.MySql => nameof(MYAddDreamDaemonLogOutput),
                    DatabaseType.PostgresSql => nameof(PGAddDreamDaemonLogOutput),
                    DatabaseType.SqlServer => nameof(MSAddDreamDaemonLogOutput),
                    DatabaseType.Sqlite => nameof(SLAddDreamDaemonLogOutput),
                    _ => BadDatabaseType(),
                };
            if (targetVersion < new Version(5, 7, 0))
                targetMigration = currentDatabaseType switch
                {
                    DatabaseType.MySql => nameof(MYAddProfiler),
                    DatabaseType.PostgresSql => nameof(PGAddProfiler),
                    DatabaseType.SqlServer => nameof(MSAddProfiler),
                    DatabaseType.Sqlite => nameof(SLAddProfiler),
                    _ => BadDatabaseType(),
                };
            if (targetVersion < new Version(4, 19, 0))
                targetMigration = currentDatabaseType switch
                {
                    DatabaseType.MySql => nameof(MYAddDumpOnHeartbeatRestart),
                    DatabaseType.PostgresSql => nameof(PGAddDumpOnHeartbeatRestart),
                    DatabaseType.SqlServer => nameof(MSAddDumpOnHeartbeatRestart),
                    DatabaseType.Sqlite => nameof(SLAddDumpOnHeartbeatRestart),
                    _ => BadDatabaseType(),
                };
            if (targetVersion < new Version(4, 18, 0))
                targetMigration = currentDatabaseType switch
                {
                    DatabaseType.MySql => nameof(MYAddUpdateSubmodules),
                    DatabaseType.PostgresSql => nameof(PGAddUpdateSubmodules),
                    DatabaseType.SqlServer => nameof(MSAddUpdateSubmodules),
                    DatabaseType.Sqlite => nameof(SLAddUpdateSubmodules),
                    _ => BadDatabaseType(),
                };
            if (targetVersion < new Version(4, 14, 0))
                targetMigration = currentDatabaseType switch
                {
                    DatabaseType.MySql => nameof(MYTruncateInstanceNames),
                    DatabaseType.PostgresSql => nameof(PGTruncateInstanceNames),
                    DatabaseType.SqlServer => nameof(MSTruncateInstanceNames),
                    DatabaseType.Sqlite => nameof(SLAddRevInfoTimestamp),
                    _ => BadDatabaseType(),
                };
            if (targetVersion < new Version(4, 10, 0))
                targetMigration = currentDatabaseType switch
                {
                    DatabaseType.MySql => nameof(MSAddRevInfoTimestamp),
                    DatabaseType.PostgresSql => nameof(PGAddRevInfoTimestamp),
                    DatabaseType.SqlServer => nameof(MSAddRevInfoTimestamp),
                    DatabaseType.Sqlite => nameof(SLAddRevInfoTimestamp),
                    _ => BadDatabaseType(),
                };
            if (targetVersion < new Version(4, 8, 0))
                targetMigration = currentDatabaseType switch
                {
                    DatabaseType.MySql => nameof(MYAddSwarmIdentifer),
                    DatabaseType.PostgresSql => nameof(PGAddSwarmIdentifer),
                    DatabaseType.SqlServer => nameof(MSAddSwarmIdentifer),
                    DatabaseType.Sqlite => nameof(SLAddSwarmIdentifer),
                    _ => BadDatabaseType(),
                };
            if (targetVersion < new Version(4, 7, 0))
                targetMigration = currentDatabaseType switch
                {
                    DatabaseType.MySql => nameof(MYAddAdditionalDDParameters),
                    DatabaseType.PostgresSql => nameof(PGAddAdditionalDDParameters),
                    DatabaseType.SqlServer => nameof(MSAddAdditionalDDParameters),
                    DatabaseType.Sqlite => nameof(SLAddAdditionalDDParameters),
                    _ => BadDatabaseType(),
                };
            if (targetVersion < new Version(4, 6, 0))
                targetMigration = currentDatabaseType switch
                {
                    DatabaseType.MySql => nameof(MYAddDeploymentColumns),
                    DatabaseType.PostgresSql => nameof(PGAddDeploymentColumns),
                    DatabaseType.SqlServer => nameof(MSAddDeploymentColumns),
                    DatabaseType.Sqlite => nameof(SLAddDeploymentColumns),
                    _ => BadDatabaseType(),
                };
            if (targetVersion < new Version(4, 5, 0))
                targetMigration = currentDatabaseType switch
                {
                    DatabaseType.MySql => nameof(MYAllowNullDMApi),
                    DatabaseType.PostgresSql => nameof(PGAllowNullDMApi),
                    DatabaseType.SqlServer => nameof(MSAllowNullDMApi),
                    DatabaseType.Sqlite => nameof(SLAllowNullDMApi),
                    _ => BadDatabaseType(),
                };
            if (targetVersion < new Version(4, 4, 0))
                targetMigration = currentDatabaseType switch
                {
                    DatabaseType.MySql => nameof(MYFixForeignKey),
                    DatabaseType.PostgresSql => nameof(PGCreate),
                    DatabaseType.SqlServer => nameof(MSRemoveSoftColumns),
                    DatabaseType.Sqlite => nameof(SLRemoveSoftColumns),
                    _ => BadDatabaseType(),
                };
 
            if (targetVersion < new Version(4, 2, 0))
                targetMigration = currentDatabaseType == DatabaseType.Sqlite ? nameof(SLRebuild) : nameof(MSFixCascadingDelete);
 
            return targetMigration;
        }
    }
}