ignore DEFERRED ops in prepare() (#241)

* execute DEFERRED ops in prepare()

* actually we should just ignore DEFERRED

* tweak

index.js

@@ -991,7 +991,11 @@ module.exports = function (log, indexesPath) {
     } else if (!op.type) {
       // to support `query(fromDB(jitdb), toCallback(cb))`
       getFullBitset(cb)
-    } else console.error('Unknown type', op)
+    } else if (op.type === 'DEFERRED') {
+      // DEFERRED only appears in this pipeline when using `prepare()` API,
+      // and only updateIndexes() is the important part in `prepare()`.
+      cb(new TypedFastBitSet())
+    } else console.error('Unknown type in jitdb executeOperation:', op)
   }
 
   function forEachLeafOperationIn(operation, fn) {
@@ -1014,7 +1018,8 @@ module.exports = function (log, indexesPath) {
           op.type === 'LTE' ||
           op.type === 'GT' ||
           op.type === 'GTE' ||
-          !op.type // e.g. query(fromDB, toCallback), or empty deferred()
+          op.type === 'DEFERRED' ||
+          !op.type // e.g. query(fromDB, toCallback), or empty deferred() result
         );
         else debug('Unknown operator type: ' + op.type)
       })

test/add.js

@@ -420,3 +420,18 @@ prepareAndRunTest('prepare an index', dir, (t, db, raf) => {
     })
   )
 })
+
+prepareAndRunTest('prepare a DEFERRED operation', dir, (t, db, raf) => {
+  const deferredQuery = {
+    type: 'DEFERRED',
+    task: (meta, cb) => {
+      cb()
+    },
+  }
+
+  db.prepare(deferredQuery, (err, duration) => {
+    t.error(err, 'no error')
+    t.equals(typeof duration, 'number')
+    t.end()
+  })
+})