Add transaction method

README.md

@@ -226,6 +226,10 @@ Destroy a batch, and releases any locks it has acquired on the db.
 
 Call this if you want to abort a batch without flushing it.
 
+#### `const output = await db.transaction((batch) => {})`
+
+Makes a new locked batch, gives a callback for operations, and flushes or closes if any error.
+
 #### `const stream = db.createReadStream([range], [options])`
 
 Make a read stream. Sort order is based on the binary value of the keys.

index.js

@@ -476,6 +476,23 @@ class Hyperbee extends ReadyResource {
     return new Batch(this, this.core, mutexify(), true, opts)
   }
 
+  async transaction (cb) {
+    const batch = this.batch()
+    let output = null
+
+    try {
+      await batch.lock()
+      output = await cb(batch)
+    } catch (err) {
+      await batch.close()
+      throw err
+    }
+
+    await batch.flush()
+
+    return output
+  }
+
   del (key, opts) {
     const b = new Batch(this, this.core, null, true, opts)
     return b.del(key, opts)

test/batches.js

@@ -284,3 +284,31 @@ test('batches close when instance closes', async function (t) {
 
   await d.close()
 })
+
+test('transaction', async function (t) {
+  const db = create()
+
+  const id = await db.transaction(async function (b) {
+    await b.put('/users/1')
+    return 123
+  })
+
+  t.is(id, 123)
+  t.ok(await db.get('/users/1'))
+})
+
+test('transaction does not commit if any error', async function (t) {
+  const db = create()
+
+  try {
+    await db.transaction(async function (b) {
+      await b.put('/users/1')
+      throw new Error('Failed')
+    })
+    t.fail('Should have failed')
+  } catch (err) {
+    t.is(err.message, 'Failed')
+  }
+
+  t.absent(await db.get('/users/1'))
+})