protoc-gen-go-sqlmap

protoc/buf plugin that turns .proto messages annotated with sqlmap extensions (table/column metadata, primary keys, foreign keys) into a <file>.sqlmap.go per proto file, containing:

• schema — schema.v1.SchemaTable/SchemaColumn values describing every table, consumed by pkg/migration to create tables (via ariga/atlas) or generate migration files.
• scanner — a <Message>Result struct per table with Scan, GetColValue, and column-list helpers, for reading rows into Go without reflection.
• query — FieldMask-aware Load<Message>/Load<Message>Rows functions that select only requested columns and eagerly load related messages (one batched IN (...) per relation, stitched in Go), consumed by pkg/query.

These are independently switchable via the plugins= parameter (see below); schema, scanner, and query are the three plugins that exist today.

Install

go install github.com/snaerverk/protoc-gen-go-sqlmap/cmd/protoc-gen-go-sqlmap@latest

protoc

protoc --go-sqlmap_out=paths=source_relative:. your.proto

Optional plugins= parameter (comma-separated, protoc-style) selects which of schema, scanner, query to emit, +-separated:

protoc --go-sqlmap_out=plugins=schema+scanner+query,paths=source_relative:. your.proto

Omit plugins= to enable all three. query requires scanner to also be enabled, since its output calls the scanner's Result type. The schema writer emits a SchemaType entry for every dialect (mysql/postgres/sqlite3) regardless — the actual dialect is chosen at runtime by migration.New, not at generation time.

buf

Add the plugin to buf.gen.yaml, either from BSR (no local install needed):

plugins:
  - remote: buf.build/snaerverk/go-sqlmap:v0.1.0
    out: pkg/generated/
    opt: [paths=source_relative, plugins=schema+scanner+query]

or as a local binary after go install:

plugins:
  - local: protoc-gen-go-sqlmap
    out: pkg/generated/
    opt: [paths=source_relative]

Annotating messages

Import sqlmap/v1/sqlmap.proto and annotate tables and columns:

syntax = "proto3";

package example;

import "sqlmap/v1/sqlmap.proto";

option go_package = "example/examplepb";

message Author {
  option (sqlmap.v1.table) = { name: "tbl_author" };
  int64 id = 1 [(sqlmap.v1.col) = { fieldname: "author_id", pk: PK_AUTO }];
  string name = 2 [(sqlmap.v1.col) = { fieldname: "author_name" }];

  // has-many: the key lives on tbl_book (author_id), not here.
  repeated Book books = 3 [(sqlmap.v1.col) = {
    foreign_key: { entity: "Book", fieldnames: ["author_id"] }
  }];
}

message Book {
  option (sqlmap.v1.table) = {
    name: "tbl_book"
    foreign_keys: [{
      fieldnames: ["author_id"]
      to: { entity: "Author", fieldnames: ["author_id"] }
      on_delete: ON_DELETE_CASCADE
    }]
  };
  int64 id = 1 [(sqlmap.v1.col) = { fieldname: "book_id", pk: PK_AUTO }];
  string title = 2 [(sqlmap.v1.col) = { fieldname: "book_title" }];
  // proto3 optional gives this field presence, so it's nullable; a bare
  // scalar has no presence and would generate NOT NULL instead.
  optional int64 author_id = 3 [(sqlmap.v1.col) = { fieldname: "author_id" }];
}

• pk: PK_AUTO for a database-generated key, PK_MAN for one the application supplies.
• A message-kind field with foreign_key is a relation: repeated is has-many (relation only, no column); a singular field is belongs-to (both a column holding the key and a relation).
• Nullability: an explicit nullable on the column wins; otherwise PKs are NOT NULL and every other column follows the proto field's presence — a proto3 optional or message-kind field has presence and is nullable, a bare proto3 scalar does not and becomes NOT NULL.
• A message-kind field without a foreign_key is stored as an embedded JSON column.

See proto/sqlmap/v1/sqlmap.proto for the full extension surface (ForeignKeyDefinition, per-dialect type overrides) and docs/design/DESIGN-SUBTYPE-TABLES.md for joined-table subtype hierarchies (oneof + (sqlmap.v1.subtypes)).

Using the generated code

db, _ := sql.Open("postgres", dsn)

// Create tables from the generated schema (or use m.Diff/ApplyPending for
// migration files instead).
m, err := migration.New(db, migration.DialectPostgres)
if err != nil {
    return err
}
if err := m.Create(ctx, examplepb.AuthorTable, examplepb.BookTable); err != nil {
    return err
}

// Load authors with their books' titles eagerly loaded, selecting only the
// columns the FieldMask asks for.
conn := query.Conn{DB: db, Dialect: query.Postgres}
authors, err := examplepb.LoadAuthor(ctx, conn,
    &fieldmaskpb.FieldMask{Paths: []string{"name", "books.title"}})

LoadAuthor also takes ...query.Cond filters (build one with query.In(col, values), which reports whether the value slice was non-empty). For row-level access without eager loading, use <Message>Result.Scan directly against GetAuthorColumns()/GetAuthorPKColumns().

Commands

task install         # go mod tidy && go install ./cmd/protoc-gen-go-sqlmap/
make install          # buf generate && go install (regenerates pkg/generated/** from proto/)
buf generate          # regenerate pkg/generated/**.pb.go from proto/
go build ./...
go test ./...                                            # golden + unit tests
go test ./pkg/generator/sqlmap/ -update                  # accept new golden output
SQLMAP_E2E=1 go test ./pkg/generator/sqlmap/ -run TestE2E # dockerized-Postgres end-to-end

Docs

• pkg.go.dev
• docs/design/DESIGN-SUBTYPE-TABLES.md — joined-table subtype hierarchies.
• docs/design/DESIGN-FILTRIFY-CONDITIONS.md — planned: translating a filtrify AST into SQL filters at runtime.

Roadmap

• Schema generation + atlas-backed migrations (create tables, diff, migration files)
• FieldMask-aware queries with eager loading (has-many and belongs-to, arbitrary depth)
• Joined-table subtypes (oneof enforced as a DB-level FK/CHECK constraint)
• Multiple dialects: PostgreSQL, MySQL/MariaDB, SQLite
• Published as a BSR remote plugin (buf.build/snaerverk/go-sqlmap)
• SQL filters translated at runtime from a filtrify AST, replacing ad-hoc query.Cond construction
• Insert/update helpers (currently out of scope; pkg/migration only creates schema, pkg/query only reads)