NeDB is not intended to be a replacement of large-scale databases such as MongoDB! Its goal is to provide you with a clean and easy way to query data and persist it to disk, for web applications that do not need lots of concurrent connections, for example a <ahref="https://github.com/louischatriot/braindead-ci"target="_blank">continuous integration and deployment server</a> and desktop applications built with <ahref="https://github.com/rogerwang/node-webkit"target="_blank">Node Webkit</a>.
I recently benchmarked NeDB against the popular client-side database <ahref="http://www.taffydb.com/"target="_blank">TaffyDB</a> and <ahref="https://github.com/louischatriot/taffydb-benchmark"target="_blank">NeDB is much, much faster</a>. That's why I created <ahref="#browser-version">a browser version</a>.
Check the <ahref="https://github.com/louischatriot/nedb/wiki/Change-log"target="_blank">change log in the wiki</a> if you think nedb doesn't behaves as the documentation describes! Most of the issues I get are due to non-latest version NeDBs.
It's a subset of MongoDB's API (the most used operations). The current API will not change, but I will add operations as they are needed. Summary of the API:
*<ahref="#creatingloading-a-database">Creating/loading a database</a>
You can use NeDB as an in-memory only datastore or as a persistent datastore. One datastore is the equivalent of a MongoDB collection. The constructor is used as follows `new Datastore(options)` where `options` is an object with the following fields:
*`filename` (optional): path to the file where the data is persisted. If left blank, the datastore is automatically considered in-memory only. It cannot end with a `~` which is used in the temporary files NeDB uses to perform crash-safe writes
issued before load is finished is buffered and will be executed when
load is done.
*`nodeWebkitAppName` (optional): if you are using NeDB from whithin a Node Webkit app, specify its name (the same one you use in the `package.json`) in this field and the `filename` will be relative to the directory Node Webkit uses to store the rest of the application's data (local storage etc.). It works on Linux, OS X and Windows.
An `_id` field will be automatically generated by NeDB. It's a 16-characters alphanumerical string that cannot be modified once it has been generated. Unlike with MongoDB, you cannot specify it (that shouldn't be a problem anyway).
You can also bulk-insert an array of documents. This operation is atomic, meaning that if one insert fails due to a unique constraint being violated, all changes are rolled back.
Use `find` to look for multiple documents matching you query, or `findOne` to look for one specific document. You can select documents based on field equality or use comparison operators (`$lt`, `$lte`, `$gt`, `$gte`, `$in`, `$nin`, `$ne`). You can also use logical operators `$or`, `$and` and `$not`. See below for the syntax.
*`$regex`: checks whether a string is matched by the regular expression. Contrary to MongoDB, the use of `$options` with `$regex` is not supported, because it doesn't give you more power than regex flags. Basic queries are more readable so only use the `$regex` operator when you need to use another operator with it (see example below)
When a field in a document is an array, NeDB first tries to see if there is an array-specific comparison function (for now there is only `$size`) being used
and tries it first. If there isn't, the query is treated as a query on every element and there is a match if at least one element matches.
*`update` specifies how the documents should be modified. It is either a new document or a set of modifiers (you cannot use both together, it doesn't make sense!)
* The modifiers create the fields they need to modify if they don't exist, and you can apply them to subdocs. Available field modifiers are `$set` to change a field's value, `$unset` to delete a field and `$inc` to increment a field's value. To work on arrays, you have `$push`, `$pop`, `$addToSet`, `$pull`, and the special `$each`. See examples below for the syntax.
NeDB supports indexing. It gives a very nice speed boost and can be used to enforce a unique constraint on a field. You can index any field, including fields in nested documents using the dot notation. For now, indexes are only used to speed up basic queries and queries using `$in`, `$lt`, `$lte`, `$gt` and `$gte`.
To create an index, use `datastore.ensureIndex(options, cb)`, where callback is optional and get passed an error if any (usually a unique constraint that was violated). `ensureIndex` can be called when you want, even after some data was inserted, though it's best to call it at application startup. The options are:
* **fieldName** (required): name of the field to index. Use the dot notation to index a field in a nested document.
* **unique** (optional, defaults to `false`): enforce field uniqueness. Note that a unique index will raise an error if you try to index two documents for which the field is not defined.
* **sparse** (optional, defaults to `false`): don't index documents for which the field is not defined. Use this option along with "unique" if you want to accept multiple documents for which it is not defined.
You can remove a previously created index with `datastore.removeIndex(fieldName, cb)`.
If your datastore is persistent, the indexes you created are persisted in the datafile, when you load the database a second time they are automatically created for you. No need to remove any `ensureIndex` though, if it is called on a database that already has the index, nothing happens.
**Note:** the `ensureIndex` function creates the index synchronously, so it's best to use it at application startup. It's quite fast so it doesn't increase startup time much (35 ms for a collection containing 10,000 documents).
As of v0.8.0, you can use NeDB in the browser! You can find it and its minified version in the repository, in the `browser-version/out` directory. You only need to require `nedb.js` or `nedb.min.js` in your HTML file and the global object `Nedb` can be used right away, with the same API as the server version:
```
<scriptsrc="nedb.min.js"></script>
<script>
var db = new Nedb(); // Create an in-memory only datastore
It has been tested and is compatible with Chrome, Safari, Firefox, IE 10, IE 9. Please open an issue if you need compatibility with IE 8/IE 7, I think it will need some work and am not sure it is needed, since most complex webapplications - the ones that would need NeDB - only work on modern browsers. To launch the tests, simply open the file `browser-version/test/index.html` in a browser and you'll see the results of the tests for this browser.
**The browser version is still young!** For now you can only use it as an in-memory database in browser environments, I'll implement persistence using indexeddb and localstorage later.
NeDB is not intended to be a replacement of large-scale databases such as MongoDB, and as such was not designed for speed. That said, it is still pretty fast on the expected datasets, especially if you use indexing. On my machine (3 years old, no SSD), with a collection containing 10,000 documents, with indexing:
* If you mostly use NeDB for logging purposes and don't want the memory footprint of your application to grow too large, you can use <ahref="https://github.com/louischatriot/nedb-logger"target="_blank">NeDB Logger</a> to insert documents in a NeDB-readable database
* If you've outgrown NeDB, switching to MongoDB won't be too hard as it is the same API. Use <ahref="https://github.com/louischatriot/nedb-to-mongodb"target="_blank">this utility</a> to transfer the data from a NeDB database to a MongoDB collection