Split queries out of multi-command string

README.md

@@ -119,6 +119,24 @@ Running in a transaction ensures each migration is atomic. Either it completes s
 
 An exception is made when `-- postgres-migrations disable-transaction` is included at the top of the migration file. This allows migrations such as `CREATE INDEX CONCURRENTLY` which cannot be run inside a transaction.
 
+### Each migration is run as a multi-command string
+
+The entire migration file is run as a single command string no matter how many queries there are.
+
+An exception is made when `-- postgres-migrations split-queries` is commented at the top of the migration file. This allows migrations to include multiple query string blocks to be run separately. Each block of queries that start with the comment `-- split-query` will be run as its own command string.
+
+Example: adding values to enums can't be run multi-command strings so rather than adding a single migration per value added the following migration will run each alter statement separately.
+```
+-- postgres-migrations disable-transaction
+-- postgres-migrations split-queries
+
+-- split-query
+ALTER TYPE eggs ADD VALUE IF NOT EXISTS 'Fried';
+
+-- split-query
+ALTER TYPE eggs ADD VALUE IF NOT EXISTS 'Scrambled';
+```
+
 ### Abort on errors
 
 If anything fails, the migration in progress is rolled back and an exception is thrown.

src/__unit__/run-migration/fixtures/split-queries.sql

@@ -0,0 +1,8 @@
+-- postgres-migrations disable-transaction
+-- postgres-migrations split-queries
+
+-- split-query
+ALTER TYPE eggs ADD VALUE IF NOT EXISTS 'Fried';
+
+-- split-query
+ALTER TYPE eggs ADD VALUE IF NOT EXISTS 'Scrambled';

src/__unit__/run-migration/index.ts

@@ -12,6 +12,7 @@ const readFile = promisify(fsReadFile)
 let normalSqlFile: string
 let normalJsFile: string
 let noTransactionSqlFile: string
+let splitQueriesSqlFile: string
 
 test.before(async () => {
   await Promise.all([
@@ -25,6 +26,12 @@ test.before(async () => {
       },
     ),
 
+    readFile(__dirname + "/fixtures/split-queries.sql", "utf8").then(
+      (contents) => {
+        splitQueriesSqlFile = contents
+      },
+    ),
+
     Promise.resolve().then(() => {
       normalJsFile = loadSqlFromJs(__dirname + "/fixtures/normal.sql.js")
     }),
@@ -152,3 +159,36 @@ test("does not roll back when there is an error inside a transactiony migration"
     )
   })
 })
+
+test("runs each query separately when instructed", (t) => {
+  const query = sinon.stub().resolves()
+  const run = runMigration(migrationTableName, {query})
+
+  const migration = buildMigration(splitQueriesSqlFile)
+  const splitQueries = migration.sql.split("-- split-query")
+
+  return run(migration).then(() => {
+    t.is(query.callCount, 4)
+    t.is(
+      query.firstCall.args[0],
+      splitQueries[0],
+      "could ignore the first entry (comments only)",
+    )
+    t.is(
+      query.secondCall.args[0],
+      splitQueries[1],
+      "should run the first migration",
+    )
+    t.is(
+      query.thirdCall.args[0],
+      splitQueries[2],
+      "should run the second migration",
+    )
+
+    t.deepEqual(
+      query.lastCall.args[0].values,
+      [migration.id, migration.name, migration.hash],
+      "should record the running of the migration in the database",
+    )
+  })
+})

src/run-migration.ts

@@ -4,6 +4,13 @@ import {Logger, Migration, BasicPgClient} from "./types"
 const noop = () => {
   //
 }
+
+const split = async (migration: Migration, client: BasicPgClient) => {
+  const queries = migration.sql.split("-- split-query")
+
+  await Promise.all(queries.map(async (query: string) => client.query(query)))
+}
+
 const insertMigration = async (
   migrationTableName: string,
   client: BasicPgClient,
@@ -30,6 +37,9 @@ export const runMigration =
       migration.sql.includes("-- postgres-migrations disable-transaction") ===
       false
 
+    const splitQueries =
+      migration.sql.includes("-- postgres-migrations split-queries") === false
+
     log(`Running migration in transaction: ${inTransaction}`)
 
     const begin = inTransaction ? () => client.query("START TRANSACTION") : noop
@@ -38,9 +48,13 @@ export const runMigration =
 
     const cleanup = inTransaction ? () => client.query("ROLLBACK") : noop
 
+    const run = splitQueries
+      ? () => client.query(migration.sql)
+      : () => split(migration, client)
+
     try {
       await begin()
-      await client.query(migration.sql)
+      await run()
       await insertMigration(migrationTableName, client, migration, log)
       await end()