#4338 pg schema upgrade (#4375)

* Method to upgrade schemas in Postgres;

Adds:
  - schemaUpgrade method which check the fields to add and delete from old schema;

* Remove the columns delete in schemaUpgrade method;

* ESLint fix and PostgresStorageAdapter.schemaUpgrade spec test

Adds:
  - Add PostgresStorageAdapter.schemaUpgrade spec tests: creates a table,
    simulates the addition of a new field and checks if its present in the database
Chores:
  - ESLint eol-last fix;

* Add check columns before and after schema upgrade, and remove the unnecessary piece of code

Add:
  - Check the right columns is present before schema upgrade and the new field is not,
    then check if the right columns is present and the new field;
Remove:
  - Piece of code unnecessary because it not need to remove diff columns;

* Optimize the schemaUpgrade method following @vitaly-t instructions, and more tests;

* If the class does not have any columns and needs an upgrade the code would
return without doing so. Fixed this.

Chore:
  - Allows class with no column to be upgraded;
  - Test for class with no columns being upgraded;

* Update PostgresStorageAdapter.js

rewriting method schemaUpgrade

* Update PostgresStorageAdapter.spec.js

* Update PostgresStorageAdapter.spec.js

spec/PostgresStorageAdapter.spec.js

@@ -1,6 +1,10 @@
 import PostgresStorageAdapter from '../src/Adapters/Storage/Postgres/PostgresStorageAdapter';
 const databaseURI = 'postgres://localhost:5432/parse_server_postgres_adapter_test_database';
 
+const getColumns = (client, className) => {
+  return client.map('SELECT column_name FROM information_schema.columns WHERE table_name = $<className>', { className }, a => a.column_name);
+};
+
 describe_only_db('postgres')('PostgresStorageAdapter', () => {
   beforeEach(done => {
     const adapter = new PostgresStorageAdapter({ uri: databaseURI })
@@ -19,4 +23,100 @@ describe_only_db('postgres')('PostgresStorageAdapter', () => {
     expect(adapter._client.$pool.ending).toEqual(true);
     done();
   });
+
+  it('schemaUpgrade, upgrade the database schema when schema changes', done => {
+    const adapter = new PostgresStorageAdapter({ uri: databaseURI });
+    const client = adapter._client;
+    const className = '_PushStatus';
+    const schema = {
+      fields: {
+        "pushTime": { type: 'String' },
+        "source": { type: 'String' },
+        "query": { type: 'String' },
+      },
+    };
+
+    adapter.createTable(className, schema)
+      .then(() => getColumns(client, className))
+      .then(columns => {
+        expect(columns).toContain('pushTime');
+        expect(columns).toContain('source');
+        expect(columns).toContain('query');
+        expect(columns).not.toContain('expiration_interval');
+
+        schema.fields.expiration_interval = { type:'Number' };
+        return adapter.schemaUpgrade(className, schema);
+      })
+      .then(() => getColumns(client, className))
+      .then(columns => {
+        expect(columns).toContain('pushTime');
+        expect(columns).toContain('source');
+        expect(columns).toContain('query');
+        expect(columns).toContain('expiration_interval');
+        done();
+      })
+      .catch(error => done.fail(error));
+  });
+
+  it('schemaUpgrade, maintain correct schema', done => {
+    const adapter = new PostgresStorageAdapter({ uri: databaseURI });
+    const client = adapter._client;
+    const className = 'Table';
+    const schema = {
+      fields: {
+        "columnA": { type: 'String' },
+        "columnB": { type: 'String' },
+        "columnC": { type: 'String' },
+      },
+    };
+
+    adapter.createTable(className, schema)
+      .then(() => getColumns(client, className))
+      .then(columns => {
+        expect(columns).toContain('columnA');
+        expect(columns).toContain('columnB');
+        expect(columns).toContain('columnC');
+
+        return adapter.schemaUpgrade(className, schema);
+      })
+      .then(() => getColumns(client, className))
+      .then(columns => {
+        expect(columns.length).toEqual(3);
+        expect(columns).toContain('columnA');
+        expect(columns).toContain('columnB');
+        expect(columns).toContain('columnC');
+        done();
+      })
+      .catch(error => done.fail(error));
+  });
+
+  it('Create a table without columns and upgrade with columns', done => {
+    const adapter = new PostgresStorageAdapter({ uri: databaseURI });
+    const client = adapter._client;
+    const className = 'EmptyTable';
+    let schema = {};
+
+    adapter.createTable(className, schema)
+      .then(() => getColumns(client, className))
+      .then(columns => {
+        expect(columns.length).toBe(0);
+
+        schema = {
+          fields: {
+            "columnA": { type: 'String' },
+            "columnB": { type: 'String' }
+          },
+        };
+
+        return adapter.schemaUpgrade(className, schema);
+      })
+      .then(() => getColumns(client, className))
+      .then(columns => {
+        expect(columns.length).toEqual(2);
+        expect(columns).toContain('columnA');
+        expect(columns).toContain('columnB');
+        done();
+      })
+      .catch(error => done.fail(error));
+  })
 });