Refactor migrations to their own files

core/db.go

@@ -2,7 +2,9 @@ package core
 
 import (
 	"database/sql"
+	"embed"
 	"fmt"
+	"log"
 
 	_ "github.com/mattn/go-sqlite3"
 )
@@ -19,56 +21,95 @@ type Item struct {
 	time    int
 }
 
+//go:embed sql/*.sql
+var migrations embed.FS
+
+// Idempotently initialize the database. Safe to call unconditionally.
 func InitDatabase(db *sql.DB) error {
-	db.Exec(`
-		create table migrations (name text) strict;
-	`)
-
-	return nil
-}
-
-func MigrateDatabase(db *sql.DB) error {
 	rows, err := db.Query(`
-		select name from migrations;
+		select exists (
+			select 1
+			from sqlite_master
+			where type = 'table'
+			and name = 'migrations'
+		)
 	`)
 	if err != nil {
 		return err
 	}
 
-	complete := map[string]bool{}
+	var exists bool
+	for rows.Next() {
+		rows.Scan(&exists)
+	}
 
+	if exists {
+		return nil
+	}
+
+	err = ApplyMigration(db, "0000_baseline.sql")
+	return err
+}
+
+// Get the names of existing migrations that haven't been applied yet.
+func GetPendingMigrations(db *sql.DB) ([]string, error) {
+	allMigrations, err := migrations.ReadDir("sql")
+	if err != nil {
+		return nil, err
+	}
+
+	complete := map[string]bool{}
+	for _, mig := range allMigrations {
+		complete[mig.Name()] = false
+	}
+
+	rows, err := db.Query("select name from migrations")
+	if err != nil {
+		return nil, err
+	}
 	for rows.Next() {
 		var name string
-		err = rows.Scan(&name)
-		if err != nil {
-			return err
-		}
+		rows.Scan(&name)
 		complete[name] = true
 	}
 
-	if !complete["0000_initial_schema"] {
-		_, err = db.Exec(`
-			create table sources(name text) strict;
-			create table items(
-				source text not null,
-				id text not null,
-				created int not null default (unixepoch()),
-				active int,
-				title text,
-				author text,
-				body text,
-				link text,
-				time int,
-				primary key (source, id),
-				foreign key (source) references sources (name) on delete cascade
-			) strict;
-			insert into migrations (name) values ('0000_initial_schema');
-		`)
+	var pending []string
+	for name, isComplete := range complete {
+		if !isComplete {
+			pending = append(pending, name)
+		}
+	}
+
+	return pending, nil
+}
+
+// Apply a migration by name.
+func ApplyMigration(db *sql.DB, name string) error {
+	data, err := migrations.ReadFile("sql/" + name)
+	if err != nil {
+		log.Fatalf("Missing migration %s", name)
+	}
+	log.Printf("Applying migration %s", name)
+	_, err = db.Exec(string(data))
+	if err != nil {
+		return err
+	}
+	_, err = db.Exec("insert into migrations (name) values (?)", name)
+	return err
+}
+
+// Apply all pending migrations.
+func MigrateDatabase(db *sql.DB) error {
+	pending, err := GetPendingMigrations(db)
+	if err != nil {
+		return err
+	}
+	for _, name := range pending {
+		err = ApplyMigration(db, name)
 		if err != nil {
 			return err
 		}
 	}
-
 	return nil
 }
 

core/db_test.go

@@ -23,17 +23,40 @@ func EphemeralDb(t *testing.T) *sql.DB {
 	return db
 }
 
+func TestInitIdempotency(t *testing.T) {
+	db, err := sql.Open("sqlite3", ":memory:")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer db.Close()
+	if err = InitDatabase(db); err != nil {
+		t.Fatal(err)
+	}
+	if err = InitDatabase(db); err != nil {
+		t.Fatal(err)
+	}
+}
+
 func TestMigrations(t *testing.T) {
 	db := EphemeralDb(t)
 	defer db.Close()
 
-	var count int
-	row := db.QueryRow("select count(name) from migrations")
-	if err := row.Scan(&count); err != nil {
+	allMigrations, err := migrations.ReadDir("sql")
+	if err != nil {
 		t.Fatal(err)
 	}
-	if count != 1 {
-		t.Fatalf("Unexpected migration count: %d", count)
+
+	rows, err := db.Query("select name from migrations")
+	if err != nil {
+		t.Fatal(err)
+	}
+	count := 0
+	for rows.Next() {
+		count += 1
+	}
+
+	if count != len(allMigrations) {
+		t.Fatalf("Expected %d migrations, got %d", len(allMigrations), count)
 	}
 }
 

core/sql/0000_baseline.sql

@@ -0,0 +1 @@
+create table migrations (name text) strict;

core/sql/0001_initial_schema.sql

@@ -0,0 +1,14 @@
+create table sources(name text) strict;
+create table items(
+    source text not null,
+    id text not null,
+    created int not null default (unixepoch()),
+    active int not null,
+    title text,
+    author text,
+    body text,
+    link text,
+    time int,
+    primary key (source, id),
+    foreign key (source) references sources (name) on delete cascade
+) strict;