Directing MongoDB Query Results to a File

The syntax for querying a MongoDB database and directing the results to a file is:

mongo server/database –eval "query" >> outputfile

where “server/database” is the address of the MongoDB database, “query” is the MongoDB command to execute, and “outputfile” is the file to which to direct the output.

Each of the following examples assumes that MongoDB has been installed in the C:\MongoDB folder.

Running this command…

C:\>mongodb\bin\mongo localhost/mydb –eval "db.docs.count()" >> counttest.txt

… will result in a file named counttest.txt that has contents similar to the following:

MongoDB shell version: 2.4.8
connecting to: localhost/mydb
1979179

For queries that will return JSON objects, be sure to wrap the command in the printjson() function, as in this example:

C:\>mongodb\bin\mongo localhost/mydb –eval "printjson(db.docs.findOne())" >> selectone.json

If the command is not wrapped by printjson, the resulting file will contain something like this:

MongoDB shell version: 2.4.8
connecting to: localhost/mydb
[object Object]

Notice that instead of the contents of the JSON object, the file simply contains the text [object Object].  However, if printjson is used, then the contents of the file will contain the actual JSON object, as shown here:

MongoDB shell version: 2.4.8
connecting to: localhost/mydb
{
     "_id" : ObjectId("528b7c7b594d11167ecdd1a7"),
     "leaf_num" : "0"
}

Here is an example that shows the use of a more complicated command.  It performs an aggregation and returns the results as JSON (notice the use of printjson):

C:\>mongodb\bin\mongo localhost/mydb –eval "printjson(db.docs.group( { key: {scan_id: 1}, reduce: function(cur, result) {result.count += 1 }, initial: {count:0}}))" >> MongoCount.txt

For this example, the contents of the MongoCount.txt file are:

MongoDB shell version: 2.4.8
connecting to: localhost/mydb
[
     {
          "scan_id" : "01A23374-4D72-4A06-9B88-EF74D0ACEE5D",
          "count" : 151
     },
     {
          "scan_id" : "0245B979-D3D6-4B01-83E1-E8D1D2ADA255",
          "count" : 250

     },
     {
          "scan_id" : "0330266.0001.002.umich.edu",
          "count" : 164
     },
     {
          "scan_id" : "03polybiblionrevue55sociuoft",
          "count" : 290
     }
]

Advertisements

2 Responses to Directing MongoDB Query Results to a File

  1. Rio says:

    you don’t use a dbs? how can i use one of the dbs before execute the query?

    • mlichtenberg says:

      In the examples I have given, the names of the server and database against which to run the query are the first parameters specified. So in the command…

      mongo localhost/mydb –eval “db.docs.count()” >> counttest.txt

      …”localhost” is the name of the server, and “mydb” is the name of the database. There is no need to issue an explicit “use mydb” statement.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: