(#398) - reuse PouchDB object between calls

lib/create-or-delete-dbs.js

@@ -0,0 +1,52 @@
+'use strict';
+
+// unified access to creating/deleting PouchDB databases,
+// to re-use PouchDB objects and avoid race conditions
+
+var Promise = require('pouchdb-promise');
+var PouchMap = require('pouchdb-collections').Map;
+
+var promiseChain = Promise.resolve();
+
+// do all creations/deletions in a single global lock
+// obviously this makes this operation slow... but hopefully you aren't
+// creating and destroying a lot of databases all the time
+function doSequentially(fun) {
+  promiseChain = promiseChain.then(fun);
+  return promiseChain;
+}
+
+function getOrCreateDB(PouchDB, dbName) {
+  var map = PouchDB.__dbCacheMap;
+  if (!map) {
+    // cache DBs to avoid costly re-allocations
+    map = PouchDB.__dbCacheMap = new PouchMap();
+  }
+  return doSequentially(function () {
+    var db = map.get(dbName);
+    if (db) {
+      return db;
+    }
+    db = new PouchDB(dbName);
+    map.set(dbName, db);
+    return db;
+  });
+}
+
+function deleteDB(PouchDB, dbName, opts) {
+  return doSequentially(function () {
+    var dbCache = PouchDB.__dbCacheMap;
+    var db = dbCache && dbCache.get(dbName);
+    if (!db) {
+      // if the db wasn't cached, we may still need to destroy it
+      // if it's saved to disk
+      return PouchDB.destroy(dbName, opts);
+    }
+    // if this db was cached, we need to remove it from the cache immediately
+    dbCache.delete(dbName);
+    return db.destroy(opts);
+  });
+}
+
+exports.getOrCreateDB = getOrCreateDB;
+exports.deleteDB = deleteDB;

lib/db-wrapper.js

@@ -19,10 +19,13 @@ DatabaseWrapper.prototype.wrap = function (name, db) {
   if (typeof db === 'undefined') {
     throw new Error("no db defined!");
   }
+  if (db.__wrappedByExpressPouch) {
+    // dbs are cached, so it might already be wrapped
+    return Promise.resolve(db);
+  }
+  db.__wrappedByExpressPouch = true;
   return utils.callAsyncRecursive(this._wrappers, function (wrapper, next) {
-    return Promise.resolve().then(function () {
-      return wrapper(name, db, next);
-    });
+    return Promise.resolve(wrapper(name, db, next));
   }).then(function () {
     // https://github.com/pouchdb/pouchdb/issues/1940
     delete db.then;

lib/replicator.js

@@ -2,6 +2,7 @@
 
 var Promise = require('pouchdb-promise');
 var utils = require('./utils');
+var getOrCreateDB = require('./create-or-delete-dbs').getOrCreateDB;
 
 module.exports = function enableReplicator(app) {
   var db, PouchDB;
@@ -55,10 +56,10 @@ module.exports = function enableReplicator(app) {
 
       return serialExecution(function () {
         var name = getReplicatorDBName();
-        db = new PouchDB(name);
-
-        PouchDB.on('destroyed', onDestroy);
-        return db.startReplicatorDaemon();
+        return getOrCreateDB(PouchDB, name).then(function (db) {
+          PouchDB.on('destroyed', onDestroy);
+          return db.startReplicatorDaemon();
+        });
       });
     },
     stop: function () {

lib/routes/db.js

@@ -5,7 +5,8 @@ var startTime     = new Date().getTime(),
     wrappers      = require('pouchdb-wrappers'),
     mkdirp        = require('mkdirp'),
     pathResolve   = require('path').resolve,
-    cleanFilename = require('../clean-filename');
+    cleanFilename = require('../clean-filename'),
+    deleteDB      = require('../create-or-delete-dbs').deleteDB;
 
 module.exports = function (app) {
   // Create a database.
@@ -63,7 +64,7 @@ module.exports = function (app) {
   });
 
   // Delete a database
-  app.delete('/:db', function (req, res, next) {
+  app.delete('/:db', function (req, res) {
     if (req.query.rev) {
       return utils.sendJSON(res, 400, {
         error: 'bad_request',
@@ -73,13 +74,12 @@ module.exports = function (app) {
         )
       });
     }
-    var name = cleanFilename(req.params.db);
-    req.PouchDB.destroy(name, utils.makeOpts(req), function (err, info) {
-      if (err) {
-        return utils.sendError(res, err);
-      }
 
+    var dbName = cleanFilename(req.params.db);
+    deleteDB(req.PouchDB, dbName, utils.makeOpts(req)).then(function () {
       utils.sendJSON(res, 200, {ok: true});
+    }, function (err) {
+      utils.sendError(res, err);
     });
   });
 

lib/utils.js

@@ -5,6 +5,7 @@ var rawBody = require('raw-body');
 var Promise = require('pouchdb-promise');
 var mkdirp = require('mkdirp');
 var cleanFilename = require('./clean-filename');
+var getOrCreateDB = require('./create-or-delete-dbs').getOrCreateDB;
 
 //shared middleware
 
@@ -75,18 +76,18 @@ exports.setDBOnReq = function (dbName, dbWrapper, req, res, next) {
         reason: 'no_db_file'
       });
     }
-    var db = new req.PouchDB(dbName);
-
-    // temporary workaround for https://github.com/pouchdb/pouchdb/issues/5668
-    // see also https://github.com/pouchdb/express-pouchdb/issues/274
-    if (/\//.test(dbName)) {
-      var path = db.__opts.prefix ? db.__opts.prefix + dbName : dbName;
-      mkdirp.sync(pathResolve(path));
-    }
+    getOrCreateDB(req.PouchDB, dbName).then(function (db) {
+      // temporary workaround for https://github.com/pouchdb/pouchdb/issues/5668
+      // see also https://github.com/pouchdb/express-pouchdb/issues/274
+      if (/\//.test(dbName)) {
+        var path = db.__opts.prefix ? db.__opts.prefix + dbName : dbName;
+        mkdirp.sync(pathResolve(path));
+      }
 
-    dbWrapper.wrap(dbName, db).then(function () {
-      req.db = db;
-      next();
+      dbWrapper.wrap(dbName, db).then(function () {
+        req.db = db;
+        next();
+      });
     });
   });
 };

package.json

@@ -25,6 +25,7 @@
     "on-finished": "^2.3.0",
     "pouchdb-all-dbs": "^1.0.2",
     "pouchdb-auth": "^2.1.1",
+    "pouchdb-collections": "6.1.2",
     "pouchdb-find": "^0.10.3",
     "pouchdb-list": "^1.1.0",
     "pouchdb-promise": "6.1.2",