Fluentmigrator New Database Provider

Adding a new database provider to FluentMigrator

FluentMigrator turns fluent C# expressions (Create.Table(...), Alter.Column(...)) into SQL via an IMigrationGenerator, and executes/introspects via an IMigrationProcessor. Every supported engine lives in its own src/FluentMigrator.Runner.<Db>/ project and its own test/FluentMigrator.Tests/{Unit/Generators,Integration/Processors}/<Db>/ folders.

The single most common failure when adding a provider is writing generator code first and discovering halfway through that the engine cannot do ALTER COLUMN ... TYPE, has no schemas, or cannot add a primary key after CREATE TABLE. Those discoveries then get hard-coded ad hoc. So the workflow here is deliberately research → ADR → tests → code, not the other way round. Do not skip the ADR phase.

Reference files (read when you reach that phase):

• references/adr-template.md — the ADR skeleton with the full IMigrationGenerator support matrix, DbType map table, and introspection-query table to fill in.
• references/touchpoints.md — every file in the repo that must be touched for a provider to be fully wired (DI, CLI, console, MSBuild, analyzers, docs, CI).
• references/code-skeletons.md — annotated C# skeletons for each class and test.
• references/testcontainers.md — sourcing Docker images, official Testcontainers.* modules vs. ContainerBuilder, wait strategies, licences/arch caveats, CI wiring.

Phase 0 — Orient in the repo (10 minutes, always)

Before writing anything, look at the two closest existing providers and copy their shape. Pick by dialect family, not by popularity:

Redshift is the smallest complete provider (nine files) and the best template for a first pass. Snowflake shows options (SnowflakeOptions), a batch parser, and quoting toggles. Read at least:

src/FluentMigrator.Runner.Redshift/**                   (whole project — it's small)
src/FluentMigrator.Runner.Core/Generators/Generic/GenericGenerator.cs
src/FluentMigrator.Runner.Core/Generators/Base/ColumnBase.cs
src/FluentMigrator.Runner.Core/Generators/Base/TypeMapBase.cs
src/FluentMigrator.Runner.Core/Processors/GenericProcessorBase.cs
src/FluentMigrator/ProcessorId.cs  and  src/FluentMigrator/GeneratorIdConstants.cs
adr/proposed/DuckDB.md                                   (a complete new-provider ADR)
test/FluentMigrator.Tests/Containers/ContainerBase.cs
test/FluentMigrator.Tests/Integration/IntegrationTestsSetup.cs
test/FluentMigrator.Tests/appsettings.json

Also check adr/proposed/ for an existing ADR about the target engine (e.g. DuckDB.md, ApacheFlightSQL.md covers Doris/StarRocks/Dremio/InfluxDB). If one exists, update it rather than writing a second one.

Phase 1 — Research the engine (before any code)

Answer every question below from the engine's official documentation (link the pages; the ADR needs a References section). Do not rely on memory — dialect details change between versions and most wrong generator code comes from a half-remembered syntax.

1. Driver. Which ADO.NET DbProviderFactory exists? Package name, assembly name, fully-qualified factory type, and whether it has a .Instance static or needs reflection. Does it support .NET Framework 4.8 (the runner projects multi-target net48;netstandard2.0) and NativeAOT/trimming (TrimAot.props)? Is the licence compatible with Apache-2.0 redistribution as a transitive dependency?
2. Naming hierarchy. database/catalog → schema → table? Two-level only? Does CREATE SCHEMA exist, or is "schema" really "database" (MySQL family)? What is the default schema name (public, dbo, main, PUBLIC)? Is it case-folding upper, lower, or preserved? Max identifier length?
3. Quoting. Identifier quote characters (", `, []), how a quote is escaped inside an identifier, string-literal escaping, boolean/date/guid literal syntax, CURRENT_TIMESTAMP / UTC-now / new-GUID function names.
4. DDL support matrix. Go through every IMigrationGenerator.Generate(...) overload (there are 24 — the template lists them) and mark ✅ / ⚠️ / ❌ with the exact syntax. Pay special attention to the operations that commonly differ: ALTER COLUMN (type change, nullability, default — three separate statements on many engines), RENAME TABLE vs ALTER TABLE ... RENAME TO, adding a primary key after creation, DROP CONSTRAINT by name, IF [NOT] EXISTS variants, sequences, identity/auto-increment syntax, computed columns, column descriptions/comments, clustered/covering/filtered indexes, foreign key ON DELETE/UPDATE rules (SET DEFAULT is often missing), transactional DDL (does a failed migration roll back DDL?), and statement batching/separators.
5. Type map. DbType → native type for all 27 DbType values, including sized variants and their max sizes (VARCHAR(n) cap, DECIMAL max precision, binary cap).
6. Introspection. SQL for schema/table/column/constraint/index/sequence/default exists. Prefer information_schema; fall back to engine catalog tables.
7. Container. Is there an official Docker image? An official Testcontainers.<Db> NuGet module? Licence acceptance flag? Only amd64? See references/testcontainers.md.

Phase 2 — Write the ADR first

Create adr/proposed/<Db>.md from references/adr-template.md. The ADR is the design contract: the support matrix in it dictates which Generate methods get overridden, which return CompatibilityMode.HandleCompatibility("..."), and which unit tests assert a throw in STRICT mode. Reviewers (and future maintainers) read the ADR to understand why the generator does something odd; without it, every dialect quirk looks like a bug.

The ADR must contain, in this order: Status, Context (use cases, driver, connection string format, schema model), Research Findings (DDL matrix, type map, introspection queries), Architecture Decision (project structure, NuGet deps, one subsection per class listing the overrides and the reason for each), Unsupported Operations Summary, Integration Tests (container or embedded strategy, test infrastructure changes), References, Conclusion. adr/proposed/DuckDB.md is the worked example; match its level of detail.

Commit the ADR as its own commit (or open a draft PR with only the ADR) so the design can be discussed before implementation. Update the ADR whenever implementation reveals the research was wrong — the matrix in the merged ADR must match the shipped code.

Phase 3 — Scaffold the project

Follow references/touchpoints.md for the exhaustive list. The core files:

src/FluentMigrator.Runner.<Db>/
├── FluentMigrator.Runner.<Db>.csproj          copy Redshift's; RootNamespace=FluentMigrator.Runner
├── <Db>RunnerBuilderExtensions.cs             Add<Db>() DI registration
├── Generators/<Db>/
│   ├── I<Db>TypeMap.cs  : ITypeMap
│   ├── <Db>TypeMap.cs   : TypeMapBase
│   ├── <Db>Quoter.cs    : GenericQuoter
│   ├── <Db>Column.cs    : ColumnBase<I<Db>TypeMap>
│   ├── <Db>DescriptionGenerator.cs : GenericDescriptionGenerator (or reuse EmptyDescriptionGenerator)
│   └── <Db>Generator.cs : GenericGenerator
└── Processors/<Db>/
    ├── <Db>DbFactory.cs : ReflectionBasedDbFactory
    ├── <Db>Options.cs   (only if the provider needs options, e.g. quoting toggle)
    └── <Db>Processor.cs : GenericProcessorBase

Then add ProcessorIdConstants.<Db> and GeneratorIdConstants.<Db> (use nameof(<Db>); add aliases like "IBM DB2" only when users would type them), add the project to FluentMigrator.sln, and register .Add<Db>() in the four aggregator call sites (FluentMigrator.Runner, DotNet.Cli, Console, MSBuild) plus the test harness call sites. Package versions go in Directory.Packages.props (central package management — no Version= on PackageReference).

Driver loading is not a per-provider choice — NativeAOT decides it. Every runner project imports TrimAot.props (IsAotCompatible, IsTrimmable, VerifyReferenceAotCompatibility on net8.0), and ReflectionBasedDbFactory refuses to probe by name when AotSupport.IsDynamicCodeSupported is false. The only path that survives AOT is a TestEntry whose third argument is a constant-string () => Type.GetType("<Namespace>.<FactoryType>, <AssemblyName>") — the trimmer can statically resolve that, and TryCreateFromPreloadedType runs before the dynamic-code gate. So:

• Every TestEntry must carry that lambda. A two-argument TestEntry works on JIT and silently returns "no factory found" under AOT.
• The runner package does not hard-reference the driver; the consuming application references it, which is what makes Type.GetType resolve. This is the SQLite/Postgres/ Snowflake pattern and the reason the runner packages stay driver-version-agnostic.
• If the driver itself is not trim/AOT-safe, say so in the ADR, add the provider to the AOT smoke tests anyway to prove the runner is fine, and document the limitation on the provider docs page. Do not disable TrimAot.props for the project.
• A driver whose factory has neither a static Instance member nor a public parameterless constructor cannot be created by TryCreateFromPreloadedType; that is a blocker to raise in the ADR, not something to work around with reflection.

Phase 4 — Write the unit tests before the generator

Unit tests for generators are pure string assertions and need no database, so write them first from the ADR's matrix and let them fail. Create test/FluentMigrator.Tests/Unit/Generators/<Db>/ with one class per base test class:

Every abstract test must be overridden — the base classes are the contract. For an operation the ADR marks ❌, the override asserts the CompatibilityMode behaviour: STRICT → Assert.Throws<DatabaseOperationNotSupportedException>, LOOSE → result.ShouldBeEmpty(). Use GeneratorTestHelper.Get*Expression() to build expressions and Shouldly's ShouldBe on the exact SQL string, statement terminator included. Expected strings come straight from the ADR matrix; if you find yourself inventing SQL while writing a test, go back and fix the ADR.

Also add the new types to the three cross-provider unit tests that enumerate every provider: Unit/Runners/DatabaseIdentifierTests.cs ([TestCase] mapping processor/generator types to their id constants), Unit/Processors/ProcessorConstructorSelectionTests.cs, and Unit/Runners/DatabaseIdConstantsSelectionTests.cs.

Phase 5 — Implement Generator → Quoter → TypeMap → Column

Implement in the order the unit tests fail. Guidance per class (skeletons in references/code-skeletons.md):

• TypeMap: SetupTypeMaps() calls SetTypeMap(DbType, template) and SetTypeMap(DbType, template, maxSize); use $size / $precision placeholders. Register the unsized default first, then sized variants in ascending size order.
• Quoter: override OpenQuote/CloseQuote/escape strings only if not "; override FormatSystemMethods, FormatDateTime, FormatBool, FormatGuid, QuoteSchemaName (return empty when schemas are unsupported) as the ADR dictates.
• Column: override FormatIdentity (required), and FormatNullable, FormatDefaultValue, FormatPrimaryKey, FormatCollation, ClauseOrder when the engine orders clauses differently. ShouldPrimaryKeysBeAddedSeparately controls inline vs. ALTER TABLE ADD CONSTRAINT.
• Generator: prefer overriding the format-string properties (RenameTable, AlterColumn, AddColumn, DropIndex, ...) over overriding Generate(...) methods; override Generate only when the statement shape differs, and call CompatibilityMode.HandleCompatibility(message) for ❌ rows. Set GeneratorId and GeneratorIdAliases. Multi-statement results (e.g. column + description) end each statement with AppendSqlStatementEndToken.

Do not invent "generic" fallbacks for unsupported features. An engine that cannot change a column type should say so via CompatibilityMode, not emit a drop-and-recreate the user did not ask for (unless the ADR explicitly decides that, as the SQLite provider does for table rebuilds).

Phase 6 — Processor + DbFactory + integration tests

The processor is mostly introspection SQL plus Read/Exists/Execute boilerplate copied verbatim from Redshift/Postgres. Implement DatabaseType, DatabaseTypeAliases, both constructors (the IMigrationConnectionFactory one marked [ActivatorUtilitiesConstructor]; the IConnectionStringAccessor one [Obsolete]), and the seven *Exists methods using the ADR's queries with FormatToSafeName / FormatToSafeSchemaName for escaping. Override transaction methods only when the engine lacks transactional DDL.

Integration tests live in test/FluentMigrator.Tests/Integration/Processors/<Db>/ and mirror the unit layout against Integration/Processors/Base*Tests.cs (table, column, constraint, index, schema, sequence, schema-extensions, plus <Db>ProcessorTests and optionally <Db>MigrationRunnerTests). Each class:

• carries [Category("Integration")] [Category("<Db>")];
• calls IntegrationTestOptions.<Db>.IgnoreIfNotEnabled() in setup so the suite passes on machines without the engine;
• builds its own ServiceProvider via ServiceCollectionExtensions.CreateServices() .ConfigureRunner(r => r.Add<Db>()) with a PassThroughConnectionStringReader;
• uses a Helpers/<Db>TestTable.cs (and <Db>TestSequence.cs) IDisposable helper that creates a uniquely-named table in setup and drops it on dispose.

Wire the options: add a <Db> block to appsettings.json with IsEnabled: false (and ContainerEnabled: false for server engines), add public static DatabaseServerOptions <Db> => GetOptions(ProcessorIdConstants.<Db>); to IntegrationTestOptions.cs, add a ProcessorTestCase<<Db>Processor> entry to Integration/TestCases/ProcessorTestCaseSource.cs, and add .Add<Db>() to IntegrationTestBase.ExecuteWithProcessor.

For server engines, add test/FluentMigrator.Tests/Containers/<Db>Container.cs extending ContainerBase (three overrides: ServerOptions, Port, Build()), add it to the Task.WhenAll list in IntegrationTestsSetup.cs, and enable it in .github/workflows/pull-requests.yaml via the FM_TestConnectionStrings__<Db>__* environment variables on the Linux matrix leg. Everything about choosing and configuring the image is in references/testcontainers.md — read it before writing Build(). Embedded engines skip the container entirely and follow the SQLite pattern.

Run locally with the container enabled before pushing:

FM_TestConnectionStrings__<Db>__IsEnabled=true \
FM_TestConnectionStrings__<Db>__ContainerEnabled=true \
dotnet test test/FluentMigrator.Tests --framework net8.0 --filter "Category=<Db>"

Phase 7 — Finish the PR

• Update the ADR to match reality and, once merged, the maintainers move it to adr/implemented/; leave it in adr/proposed/ in the PR.
• Add the provider to docs-website/providers/ (own page for a major engine, or a section in others.md), including connection-string format, Add<Db>() usage, the unsupported-operations table copied from the ADR, and any <Db>Options.
• Add a ### New entry to CHANGELOG.md under the unreleased heading, and your name under ### Contributors.
• Add <Db> to SqlDialect in src/FluentMigrator.Analyzers/Analysis/SqlDialect.cs (and SqlDialectResolver / SqlLiteralSyntax) if the engine's literal syntax matters to the Roslyn analyzers.
• Confirm dotnet pack package validation passes — the net48 target and public API baseline are checked on the Windows CI leg.
• PR description: link the ADR, list the ❌ operations, state which CI legs run the container, and say how you verified against a real instance.

Review checklist (use when reviewing someone else's provider PR)

• ADR exists, was written before code, and its matrix matches the overrides.
• Every abstract base test is overridden; ❌ operations test both compatibility modes.
• No Generate override silently returns string.Empty without going through CompatibilityMode.HandleCompatibility.
• ProcessorIdConstants/GeneratorIdConstants added and covered by DatabaseIdentifierTests.
• All aggregator Add*() call sites updated (runner, CLI, console, MSBuild, tests).
• Container uses .WithReuse(true), a real wait strategy, and pinned image tag; IsEnabled defaults to false in appsettings.json.
• Every TestEntry has the constant-string Type.GetType lambda (AOT path); no hard driver PackageReference in the runner project.
• Docs page, CHANGELOG, and Directory.Packages.props updated.