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Migrations at start-up: SQLite and PostgreSQL

Every file of the SQLite and PostgreSQL versions side by side, with the lines that differ marked.

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Configuration

sgl.yamldiffers
SQLite
PostgreSQL
1version: 1
1version: 1
2
2
3databases:
3databases:
4 - name: harbour
4 - name: harbour
5 dialect: sqlite
5 dialect: postgres
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
11 driver: database/sql
12 migrate:
13 dsn: ${env:DATABASE_URL}

Migrations

db/migrations/0001_boats.up.sqldiffers
SQLite
PostgreSQL
1CREATE TABLE boats (
1CREATE TABLE boats (
2 id INTEGER PRIMARY KEY,
2 id BIGINT GENERATED BY DEFAULT AS IDENTITY PRIMARY KEY,
3 name TEXT NOT NULL
3 name TEXT NOT NULL
4);
4);
db/migrations/0001_boats.down.sqlidentical
SQLite
PostgreSQL
1DROP TABLE boats;
1DROP TABLE boats;
db/migrations/0002_boat_home_port.up.sqlidentical
SQLite
PostgreSQL
1ALTER TABLE boats ADD COLUMN home_port TEXT NOT NULL DEFAULT 'Padstow';
1ALTER TABLE boats ADD COLUMN home_port TEXT NOT NULL DEFAULT 'Padstow';
db/migrations/0002_boat_home_port.down.sqlidentical
SQLite
PostgreSQL
1ALTER TABLE boats DROP COLUMN home_port;
1ALTER TABLE boats DROP COLUMN home_port;

Queries

AddBoatdiffers
SQLite · db/queries/boats.sql
PostgreSQL · 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
SQLite · db/queries/boats.sql
PostgreSQL · 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

AddBoatidentical
SQLite
PostgreSQL
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}
ListBoatsidentical
SQLite
PostgreSQL
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
SQLite
PostgreSQL
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/sqlite/027_migrations_at_startup/internal/store"
10 "seagull.sh/seagull/examples/postgres/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_sqlite"
12 "seagull.sh/seagull/sdk/migrate/migrate_backend_postgres"
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_sqlite.New() is the SQLite backend: it knows how to create the history
42 // migrate_backend_postgres.New() is the PostgreSQL backend: it knows how to create the
43 // table and run each migration in a transaction. NewMigrator reads the numbered *.up.sql
43 // history table and run each migration in a transaction, as PostgreSQL's DDL is
44 // and *.down.sql files from the directory inside migrations.
44 // transactional. It also holds an advisory lock while it works, so when several copies
45 migrator, err := migrate.NewMigrator(database, migrate_backend_sqlite.New(), migrations, "db/migrations")
45 // of a service start at once, one migrates and the rest wait, then find nothing to do.
46 // NewMigrator reads the numbered *.up.sql and *.down.sql files from the directory inside
47 // migrations.
48 migrator, err := migrate.NewMigrator(database, migrate_backend_postgres.New(), migrations, "db/migrations")
46 if err != nil {
49 if err != nil {
47 return err
50 return err
48 }
51 }
49
52
50 // Up applies every migration not yet in the history, in version order, and returns how
53 // Up applies every migration not yet in the history, in version order, and returns how
51 // many it applied. On a database that is up to date it applies none.
54 // many it applied. On a database that is up to date it applies none.
52 applied, err := migrator.Up(ctx)
55 applied, err := migrator.Up(ctx)
53 if err != nil {
56 if err != nil {
54 return fmt.Errorf("migrating: %w", err)
57 return fmt.Errorf("migrating: %w", err)
55 }
58 }
56 fmt.Fprintf(output, "start-up: applied %d migrations\n", applied)
59 fmt.Fprintf(output, "start-up: applied %d migrations\n", applied)
57
60
58 queries := store.New(database)
61 queries := store.New(database)
59 if err := queries.AddBoat(ctx, store.AddBoatParams{Name: boat, HomePort: "Padstow"}); err != nil {
62 if err := queries.AddBoat(ctx, store.AddBoatParams{Name: boat, HomePort: "Padstow"}); err != nil {
60 return fmt.Errorf("adding %s: %w", boat, err)
63 return fmt.Errorf("adding %s: %w", boat, err)
61 }
64 }
62 boats, err := queries.ListBoats(ctx)
65 boats, err := queries.ListBoats(ctx)
63 if err != nil {
66 if err != nil {
64 return fmt.Errorf("listing boats: %w", err)
67 return fmt.Errorf("listing boats: %w", err)
65 }
68 }
66 for _, row := range boats {
69 for _, row := range boats {
67 fmt.Fprintf(output, " %d %-9s of %s\n", row.ID, row.Name, row.HomePort)
70 fmt.Fprintf(output, " %d %-9s of %s\n", row.ID, row.Name, row.HomePort)
68 }
71 }
69 return nil
72 return nil
70}
73}
71
74
72// printHistory prints the migration history the migrator keeps in the database.
75// printHistory prints the migration history the migrator keeps in the database.
73//
76//
74// Takes database (*sql.DB) which is the migrated database.
77// Takes database (*sql.DB) which is the migrated database.
75// Takes migrations (fs.FS) which holds the migration files.
78// Takes migrations (fs.FS) which holds the migration files.
76// Takes output (io.Writer) which receives the history.
79// Takes output (io.Writer) which receives the history.
77//
80//
78// Returns error when the history cannot be read.
81// Returns error when the history cannot be read.
79func printHistory(ctx context.Context, database *sql.DB, migrations fs.FS, output io.Writer) error {
82func printHistory(ctx context.Context, database *sql.DB, migrations fs.FS, output io.Writer) error {
80 backend := migrate_backend_sqlite.New()
83 backend := migrate_backend_postgres.New()
81 migrator, err := migrate.NewMigrator(database, backend, migrations, "db/migrations")
84 migrator, err := migrate.NewMigrator(database, backend, migrations, "db/migrations")
82 if err != nil {
85 if err != nil {
83 return err
86 return err
84 }
87 }
85 statuses, err := migrator.Status(ctx)
88 statuses, err := migrator.Status(ctx)
86 if err != nil {
89 if err != nil {
87 return fmt.Errorf("reading migration status: %w", err)
90 return fmt.Errorf("reading migration status: %w", err)
88 }
91 }
89 fmt.Fprintf(output, "history in %s:\n", backend.Names().History)
92 fmt.Fprintf(output, "history in %s:\n", backend.Names().History)
90 for _, status := range statuses {
93 for _, status := range statuses {
91 fmt.Fprintf(output, " %04d %-15s applied=%t\n", status.Version, status.Name, status.Applied)
94 fmt.Fprintf(output, " %04d %-15s applied=%t\n", status.Version, status.Name, status.Applied)
92 }
95 }
93 return nil
96 return nil
94}
97}