Check table exists in current search path

* If a `migrations` table did exist in a schema outside of the
  search path, `doesTableExist` would return true but the migration
  would then fail with 'relation "migrations" does not exist'
* See https://dba.stackexchange.com/a/86098 for the details on the query
* This new query makes it possible to have one `migrations` table per
  schema

Issue #92 Migrations can't be run on multiple schemas in the same database

Co-authored-by: Remi Koenig <r.koenig@agricool.co>

Author: slifty

src/__tests__/fixtures/multiple-schemas-2/1_another.sql

@@ -0,0 +1,3 @@
+CREATE TABLE another (
+  id integer
+);

src/__tests__/fixtures/multiple-schemas/1_success.sql

@@ -0,0 +1,3 @@
+CREATE TABLE success (
+  id integer
+);

src/__tests__/migrate.ts

@@ -75,6 +75,35 @@ test("concurrent migrations - index concurrently", async (t) => {
   t.truthy(exists)
 })
 
+test("multiple schemas", async (t) => {
+  const databaseName = "migration-test-multiple-schemas"
+  const dbConfig = {
+    database: databaseName,
+    user: "postgres",
+    password: PASSWORD,
+    host: "localhost",
+    port,
+  }
+
+  await createDb(databaseName, dbConfig)
+  const client = new pg.Client(dbConfig)
+  await client.connect()
+
+  await createSchema(client, "schema_1")
+  await useSchema(client, "schema_1")
+  await migrate({ client }, "src/__tests__/fixtures/multiple-schemas")
+  const firstMigrationSucceeded = await doesTableExist(dbConfig, "success")
+  t.truthy(firstMigrationSucceeded)
+
+  await createSchema(client, "schema_2")
+  await useSchema(client, "schema_2")
+  await migrate({ client }, "src/__tests__/fixtures/multiple-schemas-2")
+  const secondMigrationSucceeded = await doesTableExist(dbConfig, "another")
+  t.truthy(secondMigrationSucceeded)
+
+  await client.end()
+})
+
 // can't test with unconnected client because `pg` just hangs on the first query...
 test("with connected client", async (t) => {
   const databaseName = "migration-test-with-connected-client"
@@ -720,3 +749,11 @@ function doesTableExist(dbConfig: pg.ClientConfig, tableName: string) {
       }
     })
 }
+
+async function createSchema(client: pg.Client, schemaName: string): Promise<void> {
+  await client.query(`CREATE SCHEMA ${schemaName};`)
+}
+
+async function useSchema(client: pg.Client, schemaName: string): Promise<void> {
+  await client.query(`SET search_path TO ${schemaName};`)
+}

src/migrate.ts

@@ -200,14 +200,13 @@ function logResult(completedMigrations: Array<Migration>, log: Logger) {
   }
 }
 
-/** Check whether table exists in postgres - http://stackoverflow.com/a/24089729 */
+/** Check whether table exists in postgres in the current search path
+ * http://stackoverflow.com/a/24089729
+ * https://dba.stackexchange.com/a/86098
+ */
 async function doesTableExist(client: BasicPgClient, tableName: string) {
-  const result = await client.query(SQL`SELECT EXISTS (
-  SELECT 1
-  FROM   pg_catalog.pg_class c
-  WHERE  c.relname = ${tableName}
-  AND    c.relkind = 'r'
-);`)
-
+  const result = await client.query(
+    SQL`SELECT to_regclass(${tableName}) is not NULL as exists;`,
+  )
   return result.rows.length > 0 && result.rows[0].exists
 }