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Migrations at start-up: MySQL and DuckDB

Every file of the MySQL and DuckDB versions side by side, with the lines that differ marked. 2 parameter or column types differ in Go.

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Configuration

sgl.yamldiffers

MySQL
DuckDB
1version: 1
1version: 1
2
2
3databases:
3databases:
4  - name: harbour
4  - name: harbour
5    dialect: mysql
5    dialect: duckdb
6    migrations: db/migrations
6    migrations: db/migrations
7    queries: db/queries
7    queries: db/queries
8    go:
8    go:
9      package: store
9      package: store
10      out: internal/store
10      out: internal/store

Migrations

db/migrations/0001_boats.up.sqldiffers

MySQL
DuckDB
1CREATE SEQUENCE boat_ids;
2
1CREATE TABLE boats (
3CREATE TABLE boats (
2    id   BIGINT      NOT NULL AUTO_INCREMENT PRIMARY KEY,
4    id   BIGINT  PRIMARY KEY DEFAULT nextval('boat_ids'),
3    name VARCHAR(50) NOT NULL
5    name VARCHAR NOT NULL
4);
6);

db/migrations/0001_boats.down.sqldiffers

MySQL
DuckDB
1DROP TABLE boats;
1DROP TABLE boats;
2DROP SEQUENCE boat_ids;

db/migrations/0002_boat_home_port.up.sqldiffers

MySQL
DuckDB
1ALTER TABLE boats ADD COLUMN home_port VARCHAR(50) NOT NULL DEFAULT 'Padstow';
1ALTER TABLE boats ADD COLUMN home_port VARCHAR DEFAULT 'Padstow';

db/migrations/0002_boat_home_port.down.sqlidentical

MySQL
DuckDB
1ALTER TABLE boats DROP COLUMN home_port;
1ALTER TABLE boats DROP COLUMN home_port;

Queries

AddBoatdiffers

MySQL · db/queries/boats.sql
DuckDB · db/queries/boats.sql
1-- sgl.query(AddBoat, exec)
1-- sgl.query(AddBoat, exec)
2INSERT INTO boats (name, home_port) VALUES (?, ?);
2INSERT INTO boats (name, home_port) VALUES ($1, $2);

ListBoatsidentical

MySQL · db/queries/boats.sql
DuckDB · db/queries/boats.sql
1-- sgl.query(ListBoats, many)
1-- sgl.query(ListBoats, many)
2SELECT id, name, home_port FROM boats ORDER BY id;
2SELECT id, name, home_port FROM boats ORDER BY id;

What sgl generates

AddBoatdiffers

MySQL
DuckDB
1func (queries *Queries) AddBoat(ctx context.Context, params AddBoatParams) error
1func (queries *Queries) AddBoat(ctx context.Context, params AddBoatParams) error
2
2
3type AddBoatParams struct {
3type AddBoatParams struct {
4	Name     string
4	Name     string
5	HomePort string
5	HomePort *string
6}
6}

ListBoatsdiffers

MySQL
DuckDB
1func (queries *Queries) ListBoats(ctx context.Context) ([]ListBoatsRow, error)
1func (queries *Queries) ListBoats(ctx context.Context) ([]ListBoatsRow, error)
2
2
3type ListBoatsRow struct {
3type ListBoatsRow struct {
4	ID       int64  `json:"id"`
4	ID       int64   `json:"id"`
5	Name     string `json:"name"`
5	Name     string  `json:"name"`
6	HomePort string `json:"home_port"`
6	HomePort *string `json:"home_port"`
7}
7}

The program

example.godiffers

MySQL
DuckDB
1package main
1package main
2
2
3import (
3import (
4	"context"
4	"context"
5	"database/sql"
5	"database/sql"
6	"fmt"
6	"fmt"
7	"io"
7	"io"
8	"io/fs"
8	"io/fs"
9
9
10	"seagull.sh/seagull/examples/mysql/027_migrations_at_startup/internal/store"
10	"seagull.sh/seagull/examples/duckdb/027_migrations_at_startup/internal/store"
11	"seagull.sh/seagull/sdk/migrate"
11	"seagull.sh/seagull/sdk/migrate"
12	"seagull.sh/seagull/sdk/migrate/migrate_backend_mysql"
12	"seagull.sh/seagull/sdk/migrate/migrate_backend_duckdb"
13)
13)
14
14
15// run starts the program twice against the same database. The first start applies both
15// run starts the program twice against the same database. The first start applies both
16// migrations before the program uses the schema; the second finds nothing to do.
16// migrations before the program uses the schema; the second finds nothing to do.
17//
17//
18// Takes database (*sql.DB) which is the database to migrate, empty or not.
18// Takes database (*sql.DB) which is the database to migrate, empty or not.
19// Takes migrations (fs.FS) which holds db/migrations, the embed.FS in main.go.
19// Takes migrations (fs.FS) which holds db/migrations, the embed.FS in main.go.
20// Takes output (io.Writer) which receives what each start did.
20// Takes output (io.Writer) which receives what each start did.
21//
21//
22// Returns error when migrating or a query fails.
22// Returns error when migrating or a query fails.
23func run(ctx context.Context, database *sql.DB, migrations fs.FS, output io.Writer) error {
23func run(ctx context.Context, database *sql.DB, migrations fs.FS, output io.Writer) error {
24	for _, boat := range []string{"Kittiwake", "Puffin"} {
24	for _, boat := range []string{"Kittiwake", "Puffin"} {
25		if err := start(ctx, database, migrations, boat, output); err != nil {
25		if err := start(ctx, database, migrations, boat, output); err != nil {
26			return err
26			return err
27		}
27		}
28	}
28	}
29	return printHistory(ctx, database, migrations, output)
29	return printHistory(ctx, database, migrations, output)
30}
30}
31
31
32// start is what the program does each time it starts: migrate first, then work. Here the
32// start is what the program does each time it starts: migrate first, then work. Here the
33// work is adding a boat and listing the harbour.
33// work is adding a boat and listing the harbour.
34//
34//
35// Takes database (*sql.DB) which is the database.
35// Takes database (*sql.DB) which is the database.
36// Takes migrations (fs.FS) which holds the migration files.
36// Takes migrations (fs.FS) which holds the migration files.
37// Takes boat (string) which names the boat to add.
37// Takes boat (string) which names the boat to add.
38// Takes output (io.Writer) which receives what happened.
38// Takes output (io.Writer) which receives what happened.
39//
39//
40// Returns error when migrating or a query fails.
40// Returns error when migrating or a query fails.
41func start(ctx context.Context, database *sql.DB, migrations fs.FS, boat string, output io.Writer) error {
41func start(ctx context.Context, database *sql.DB, migrations fs.FS, boat string, output io.Writer) error {
42	// migrate_backend_mysql.New() is the MySQL backend: it knows how to create the history
42	// migrate_backend_duckdb.New() is the DuckDB backend: it knows how to create the history
43	// table and holds a GET_LOCK advisory lock, scoped to this schema, while it works, so
43	// table, binds its own queries with $N placeholders, and runs each migration in a
44	// when several copies of a service start at once, one migrates and the rest wait, then
44	// transaction, as DuckDB DDL is transactional. The backend takes no database lock;
45	// find nothing to do. MySQL commits each CREATE or ALTER as it runs, so a migration
45	// callers must serialise migrations across migrator instances. NewMigrator reads the
46	// cannot be rolled back as a whole: keep each one to a single statement of DDL.
46	// numbered *.up.sql and *.down.sql files from the directory inside migrations.
47	// NewMigrator reads the numbered *.up.sql and *.down.sql files from the directory inside
47	migrator, err := migrate.NewMigrator(database, migrate_backend_duckdb.New(), migrations, "db/migrations")
48	// migrations.
49	migrator, err := migrate.NewMigrator(database, migrate_backend_mysql.New(), migrations, "db/migrations")
50	if err != nil {
48	if err != nil {
51		return err
49		return err
52	}
50	}
53
51
54	// Up applies every migration not yet in the history, in version order, and returns how
52	// Up applies every migration not yet in the history, in version order, and returns how
55	// many it applied. On a database that is up to date it applies none.
53	// many it applied. On a database that is up to date it applies none.
56	applied, err := migrator.Up(ctx)
54	applied, err := migrator.Up(ctx)
57	if err != nil {
55	if err != nil {
58		return fmt.Errorf("migrating: %w", err)
56		return fmt.Errorf("migrating: %w", err)
59	}
57	}
60	fmt.Fprintf(output, "start-up: applied %d migrations\n", applied)
58	fmt.Fprintf(output, "start-up: applied %d migrations\n", applied)
61
59
60	// DuckDB cannot add a NOT NULL column to an existing table, so 0002 adds home_port with
61	// a default only, and the column, like its field, may be NULL.
62	queries := store.New(database)
62	queries := store.New(database)
63	if err := queries.AddBoat(ctx, store.AddBoatParams{Name: boat, HomePort: "Padstow"}); err != nil {
63	if err := queries.AddBoat(ctx, store.AddBoatParams{Name: boat, HomePort: new("Padstow")}); err != nil {
64		return fmt.Errorf("adding %s: %w", boat, err)
64		return fmt.Errorf("adding %s: %w", boat, err)
65	}
65	}
66	boats, err := queries.ListBoats(ctx)
66	boats, err := queries.ListBoats(ctx)
67	if err != nil {
67	if err != nil {
68		return fmt.Errorf("listing boats: %w", err)
68		return fmt.Errorf("listing boats: %w", err)
69	}
69	}
70	for _, row := range boats {
70	for _, row := range boats {
71		fmt.Fprintf(output, "  %d %-9s of %s\n", row.ID, row.Name, row.HomePort)
71		homePort := "an unknown port"
72		if row.HomePort != nil {
73			homePort = *row.HomePort
74		}
75		fmt.Fprintf(output, "  %d %-9s of %s\n", row.ID, row.Name, homePort)
72	}
76	}
73	return nil
77	return nil
74}
78}
75
79
76// printHistory prints the migration history the migrator keeps in the database.
80// printHistory prints the migration history the migrator keeps in the database.
77//
81//
78// Takes database (*sql.DB) which is the migrated database.
82// Takes database (*sql.DB) which is the migrated database.
79// Takes migrations (fs.FS) which holds the migration files.
83// Takes migrations (fs.FS) which holds the migration files.
80// Takes output (io.Writer) which receives the history.
84// Takes output (io.Writer) which receives the history.
81//
85//
82// Returns error when the history cannot be read.
86// Returns error when the history cannot be read.
83func printHistory(ctx context.Context, database *sql.DB, migrations fs.FS, output io.Writer) error {
87func printHistory(ctx context.Context, database *sql.DB, migrations fs.FS, output io.Writer) error {
84	backend := migrate_backend_mysql.New()
88	backend := migrate_backend_duckdb.New()
85	migrator, err := migrate.NewMigrator(database, backend, migrations, "db/migrations")
89	migrator, err := migrate.NewMigrator(database, backend, migrations, "db/migrations")
86	if err != nil {
90	if err != nil {
87		return err
91		return err
88	}
92	}
89	statuses, err := migrator.Status(ctx)
93	statuses, err := migrator.Status(ctx)
90	if err != nil {
94	if err != nil {
91		return fmt.Errorf("reading migration status: %w", err)
95		return fmt.Errorf("reading migration status: %w", err)
92	}
96	}
93	fmt.Fprintf(output, "history in %s:\n", backend.Names().History)
97	fmt.Fprintf(output, "history in %s:\n", backend.Names().History)
94	for _, status := range statuses {
98	for _, status := range statuses {
95		fmt.Fprintf(output, "  %04d %-15s applied=%t\n", status.Version, status.Name, status.Applied)
99		fmt.Fprintf(output, "  %04d %-15s applied=%t\n", status.Version, status.Name, status.Applied)
96	}
100	}
97	return nil
101	return nil
98}
102}

Go type differences

The same SQL types map to different Go types, because each database reports them differently.

Query	Field	MySQL	DuckDB
AddBoat	parameter `home_port`	`string`	`*string`
ListBoats	column `home_port`	`string`	`*string`