In yesterday’s post MongoDB: How to backup and restore databases we looked at how to backup and restore a database, today we are going to look at how to restore a collection from a backup. Be aware that mongorestore and mongodump have to be executed from a command window in the bin directory where mongodb is. To execute the MongoDB commands you need to connect to mongodb first. On my PC this is in the directory C:NoSQLmongodbbin>
In order to get started create a new database, name it MultiCollection
You can just run this command, it will switch to the MultiCollection database if it exists or otherwise it will create the MultiCollection database
use MultiCollection
Now add these two collections
db.Blog.insert( { name : "Denis", age : 20 } )
db.Blog.insert( { name : "Abe", age : 30 } )
db.Blog.insert( { name : "John", age : 40 } )
db.Blog.insert( { name : "Xavier", age : 10 } )
db.Blog.insert( { name : "Zen", age : 50 } )
db.People.insert( { name : "AADenis", age : 0020 } )
db.People.insert( { name : "AAAbe", age : 0030 } )
db.People.insert( { name : "AAJohn", age : 0040 } )
db.People.insert( { name : "AAXavier", age : 0010 } )
db.People.insert( { name : "AAZen", age : 0050 } )
Open a new command window, navigate to your mongodb bin directory. Now execute the mongodump --db MultiCollection command
This command will backup the database into the dump directory, if this directory does not exist it will be created, in my case it will be located here C:NoSQLmongodbbindump. In the dump directory you will see a directory with the same name as the database that you are backing up
mongodump --db MultiCollection
Here is the output
connected to: 127.0.0.1 Thu Jan 31 16:16:52 DATABASE: MultiCollection to dump/MultiCollection Thu Jan 31 16:16:52 MultiCollection.Blog to dump/MultiCollection/Blog.bson Thu Jan 31 16:16:52 5 objects Thu Jan 31 16:16:52 Metadata for MultiCollection.Blog to dump/MultiCollection/Blog.metadata.json Thu Jan 31 16:16:52 MultiCollection.People to dump/MultiCollection/People.bson Thu Jan 31 16:16:52 5 objects Thu Jan 31 16:16:52 Metadata for MultiCollection.People to dump/MultiCollection/People.metadata.json C:NoSQLmongodbbin>
Now let’s add one more item to the People collection
db.People.insert( { name : "ZZZZZZ", age : 9999 } )
Time to do the restore
mongorestore dump/MultiCollection
Here is the output
connected to: 127.0.0.1
Thu Jan 31 16:20:52 dump/MultiCollection/Blog.bson
Thu Jan 31 16:20:52 going into namespace [MultiCollection.Blog]
Thu Jan 31 16:20:52 warning: Restoring to MultiCollection.Blog without dropping. Restored data will be inserted
raising errors; check your server log
5 objects found
Thu Jan 31 16:20:52 Creating index: { key: { _id: 1 }, ns: "MultiCollection.Blog", name: "_id_" }
Thu Jan 31 16:20:52 dump/MultiCollection/People.bson
Thu Jan 31 16:20:52 going into namespace [MultiCollection.People]
5 objects found
Thu Jan 31 16:20:52 Creating index: { key: { _id: 1 }, ns: "MultiCollection.People", name: "_id_" }
Let’s take a look at what we have
We should have 5 items since we did a backup before we added item 6, we restored that backup
db.People.find()
Output is here
{ "_id" : ObjectId("510adec2d9a67956d3f4a44b"), "name" : "AADenis", "age" : 16 }
{ "_id" : ObjectId("510adec2d9a67956d3f4a44c"), "name" : "AAAbe", "age" : 24 }
{ "_id" : ObjectId("510adec2d9a67956d3f4a44d"), "name" : "AAJohn", "age" : 32 }
{ "_id" : ObjectId("510adec2d9a67956d3f4a44e"), "name" : "AAXavier", "age" : 8 }
{ "_id" : ObjectId("510adec5d9a67956d3f4a44f"), "name" : "AAZen", "age" : 40 }
{ "_id" : ObjectId("510ae0b8d9a67956d3f4a451"), "name" : "ZZZZZZ", "age" : 9999 }
Something is not right, we still have 6 items. If you look back at the restore output, you will see the following warning
warning: Restoring to MultiCollection.Blog without dropping. Restored data will be inserted
raising errors; check your server log
What we have to do is drop the collections first, you do that by specifying --drop
Let’s do the restore again but now with the –drop option
mongorestore dump/MultiCollection --drop
Here is the output
connected to: 127.0.0.1
Thu Jan 31 16:25:26 dump/MultiCollection/Blog.bson
Thu Jan 31 16:25:26 going into namespace [MultiCollection.Blog]
Thu Jan 31 16:25:26 dropping
5 objects found
Thu Jan 31 16:25:26 Creating index: { key: { _id: 1 }, ns: "MultiCollection.Blog", name: "_id_" }
Thu Jan 31 16:25:26 dump/MultiCollection/People.bson
Thu Jan 31 16:25:26 going into namespace [MultiCollection.People]
Thu Jan 31 16:25:26 dropping
5 objects found
Thu Jan 31 16:25:26 Creating index: { key: { _id: 1 }, ns: "MultiCollection.People", name: "_id_" }
db.People.find()
Here are the results
{ "_id" : ObjectId("510adec2d9a67956d3f4a44b"), "name" : "AADenis", "age" : 16 }
{ "_id" : ObjectId("510adec2d9a67956d3f4a44c"), "name" : "AAAbe", "age" : 24 }
{ "_id" : ObjectId("510adec2d9a67956d3f4a44d"), "name" : "AAJohn", "age" : 32 }
{ "_id" : ObjectId("510adec2d9a67956d3f4a44e"), "name" : "AAXavier", "age" : 8 }
{ "_id" : ObjectId("510adec5d9a67956d3f4a44f"), "name" : "AAZen", "age" : 40 }
As you can see we have 5 items now
Let’s insert the same item again
db.People.insert( { name : "ZZZZZZ", age : 9999 } )
Let’s also drop the Blog collection
db.Blog.drop()
Now if you do a find nothing is there
db.Blog.find()
In order to restore a collection, you need to use the –collection option and give the collection name, you also need to specify where the backup file is. In our case it is dump/Multicollection/Blog.bson. You will also see that information from the dump output
MultiCollection.Blog to dump/MultiCollection/Blog.bson
Run the following
mongorestore --db MultiCollection --collection Blog dump/Multicollection/Blog.bson
Here is the output
connected to: 127.0.0.1
Thu Jan 31 17:01:28 dump/Multicollection/Blog.bson
Thu Jan 31 17:01:28 going into namespace [MultiCollection.Blog]
5 objects found
Thu Jan 31 17:01:28 Creating index: { key: { _id: 1 }, ns: "MultiCollection.Blog", name: "_id_" }
Since we already dropped the collection manually we didn’t have to add the drop option. Let’s see what we have in the database now, People should have 6 items and Blog should have 5 items
db.Blog.find()
{ "_id" : ObjectId("510adec1d9a67956d3f4a446"), "name" : "Denis", "age" : 20 }
{ "_id" : ObjectId("510adec1d9a67956d3f4a447"), "name" : "Abe", "age" : 30 }
{ "_id" : ObjectId("510adec2d9a67956d3f4a448"), "name" : "John", "age" : 40 }
{ "_id" : ObjectId("510adec2d9a67956d3f4a449"), "name" : "Xavier", "age" : 10 }
{ "_id" : ObjectId("510adec2d9a67956d3f4a44a"), "name" : "Zen", "age" : 50 }
db.People.find()
{ "_id" : ObjectId("510adec2d9a67956d3f4a44b"), "name" : "AADenis", "age" : 16 }
{ "_id" : ObjectId("510adec2d9a67956d3f4a44c"), "name" : "AAAbe", "age" : 24 }
{ "_id" : ObjectId("510adec2d9a67956d3f4a44d"), "name" : "AAJohn", "age" : 32 }
{ "_id" : ObjectId("510adec2d9a67956d3f4a44e"), "name" : "AAXavier", "age" : 8 }
{ "_id" : ObjectId("510adec5d9a67956d3f4a44f"), "name" : "AAZen", "age" : 40 }
{ "_id" : ObjectId("510ae75cd9a67956d3f4a453"), "name" : "ZZZZZZ", "age" : 9999 }
As you can see the People collection did not get overwritten and the Blog collection got restored
That is all for this post, if you are interested in my other MongoDB posts, you can find them here:
Install MongoDB as a Windows Service
How to sort results in MongoDB
Indexes in MongoDB: A quick overview
Multidocument updates with MongoDB
MongoDB: How to include and exclude the fields you want in results
MongoDB: How to limit results and how to page through results
Denis has been working with SQL Server since version 6.5. Although he worked as an ASP/JSP/ColdFusion developer before the dot com bust, he has been working exclusively as a database developer/architect since 2002. In addition to English, Denis is also fluent in Croatian and Dutch, but he can curse in many other languages and dialects (just ask the SQL optimizer) He lives in Princeton, NJ with his wife and three kids.
