Add MongoCollection and adaptiveCollection abstraction to MongoAdapter.

src/Adapters/Storage/Mongo/MongoCollection.js

@@ -0,0 +1,49 @@
+
+let mongodb = require('mongodb');
+let Collection = mongodb.Collection;
+
+export default class MongoCollection {
+  _mongoCollection:Collection;
+
+  constructor(mongoCollection:Collection) {
+    this._mongoCollection = mongoCollection;
+  }
+
+  // Does a find with "smart indexing".
+  // Currently this just means, if it needs a geoindex and there is
+  // none, then build the geoindex.
+  // This could be improved a lot but it's not clear if that's a good
+  // idea. Or even if this behavior is a good idea.
+  find(query, { skip, limit, sort } = {}) {
+    return this._rawFind(query, { skip, limit, sort })
+      .catch(error => {
+        // Check for "no geoindex" error
+        if (error.code != 17007 ||
+          !error.message.match(/unable to find index for .geoNear/)) {
+          throw error;
+        }
+        // Figure out what key needs an index
+        let key = error.message.match(/field=([A-Za-z_0-9]+) /)[1];
+        if (!key) {
+          throw error;
+        }
+
+        var index = {};
+        index[key] = '2d';
+        //TODO: condiser moving index creation logic into Schema.js
+        return this._mongoCollection.createIndex(index)
+          // Retry, but just once.
+          .then(() => this._rawFind(query, { skip, limit, sort }));
+      });
+  }
+
+  _rawFind(query, { skip, limit, sort } = {}) {
+    return this._mongoCollection
+      .find(query, { skip, limit, sort })
+      .toArray();
+  }
+
+  count(query, { skip, limit, sort } = {}) {
+    return this._mongoCollection.count(query, { skip, limit, sort });
+  }
+}

src/Adapters/Storage/Mongo/MongoStorageAdapter.js

@@ -1,4 +1,6 @@
 
+import MongoCollection from './MongoCollection';
+
 let mongodb = require('mongodb');
 let MongoClient = mongodb.MongoClient;
 
@@ -30,6 +32,12 @@ export class MongoStorageAdapter {
     });
   }
 
+  adaptiveCollection(name: string) {
+    return this.connect()
+      .then(() => this.database.collection(name))
+      .then(rawCollection => new MongoCollection(rawCollection));
+  }
+
   collectionExists(name: string) {
     return this.connect().then(() => {
       return this.database.listCollections({ name: name }).toArray();