读

Equality Matches¶

The following operation returns a cursor to documents in the bios collection where the field _id equals 5:

db.bios.find(
   {
      _id: 5
   }
)

Using Operators¶

The following operation returns a cursor to all documents in the bios collection where the field _id equals 5 or ObjectId("507c35dd8fada716c89d0013"):

db.bios.find(
   {
      _id: { $in: [ 5,  ObjectId("507c35dd8fada716c89d0013") ] }
   }
)

On Arrays¶

db.bios.find(
   {
     contribs: 'UNIX'
   }
)

db.bios.find(
   {
      awards: {
                $elemMatch: {
                     award: 'Turing Award',
                     year: { $gt: 1980 }
                }
      }
   }
)

On Subdocuments¶

db.bios.find(
    {
      name: {
              first: 'Yukihiro',
              last: 'Matsumoto'
            }
    }
)

{
   first: 'Yukihiro',
   aka: 'Matz',
   last: 'Matsumoto'
}

{
   last: 'Matsumoto',
   first: 'Yukihiro'
}

db.bios.find(
   {
     'name.first': 'Yukihiro',
     'name.last': 'Matsumoto'
   }
)

{
  first: 'Yukihiro',
  aka: 'Matz',
  last: 'Matsumoto'
}

{
  last: 'Matsumoto',
  first: 'Yukihiro'
}

Logical Operators¶

db.bios.find(
   { $or: [
            { 'name.first' : /^G/ },
            { birth: { $lt: new Date('01/01/1945') } }
          ]
   }
)

db.bios.find(
   {
      'name.first': /^K/,
      contribs: 'UNIX'
   }
)

Specify the Fields to Return¶

The following operation finds all documents in the bios collection and returns only the name field, the contribs field, and the _id field:

db.bios.find(
    { },
    { name: 1, contribs: 1 }
 )

Explicitly Exclude the _id Field¶

The following operation finds all documents in the bios collection and returns only the name field and the contribs field:

db.bios.find(
   { },
   { name: 1, contribs: 1, _id: 0 }
)

Return All but the Excluded Fields¶

The following operation finds the documents in the bios collection where the contribs field contains the element 'OOP' and returns all fields except the _id field, the first field in the name subdocument, and the birth field from the matching documents:

db.bios.find(
   { contribs: 'OOP' },
   { _id: 0, 'name.first': 0, birth: 0 }
)

On Arrays and Subdocuments¶

The following operation finds all documents in the bios collection and returns the the last field in the name subdocument and the first two elements in the contribs array:

db.bios.find(
   { },
   {
     _id: 0,
     'name.last': 1,
     contribs: { $slice: 2 }
   }
)

With Variable Name¶

When you assign the find() to a variable, you can type the name of the cursor variable to iterate up to 20 times [1] and print the matching documents, as in the following example:

var myCursor = db.bios.find( { _id: 1 } );

myCursor

With next() Method¶

You can use the cursor method next() to access the documents, as in the following example:

var myCursor = db.bios.find( { _id: 1 } );

var myDocument = myCursor.hasNext() ? myCursor.next() : null;

if (myDocument) {
    var myName = myDocument.name;
    print (tojson(myName));
}

To print, you can also use the printjson() method instead of print(tojson()):

if (myDocument) {
   var myName = myDocument.name;
   printjson(myName);
}

With forEach() Method¶

You can use the cursor method forEach() to iterate the cursor and access the documents, as in the following example:

var myCursor = db.bios.find( { _id: 1 } );

myCursor.forEach(printjson);

For more information on cursor handling, see:

• cursor.hasNext()
• cursor.next()
• cursor.forEach()
• cursors
• JavaScript cursor methods

Order Documents in the Result Set¶

The sort() method orders the documents in the result set.

The following operation returns all documents (or more precisely, a cursor to all documents) in the bios collection ordered by the name field ascending:

db.bios.find().sort( { name: 1 } )

sort() corresponds to the ORDER BY statement in SQL.

Limit the Number of Documents to Return¶

The limit() method limits the number of documents in the result set.

The following operation returns at most 5 documents (or more precisely, a cursor to at most 5 documents) in the bios collection:

db.bios.find().limit( 5 )

limit() corresponds to the LIMIT statement in SQL.

Set the Starting Point of the Result Set¶

The skip() method controls the starting point of the results set.

The following operation returns all documents, skipping the first 5 documents in the bios collection:

db.bios.find().skip( 5 )

Combine Cursor Methods¶

You can chain these cursor methods, as in the following examples [2]:

db.bios.find().sort( { name: 1 } ).limit( 5 )
db.bios.find().limit( 5 ).sort( { name: 1 } )

See the JavaScript cursor methods reference and your driver documentation for additional references. See Cursors for more information regarding cursors.

Specify the Fields to Return¶

The following operation finds a document in the bios collection and returns only the name field, the contribs field, and the _id field:

db.bios.findOne(
    { },
    { name: 1, contribs: 1 }
)

Return All but the Excluded Fields¶

The following operation returns a document in the bios collection where the contribs field contains the element OOP and returns all fields except the _id field, the first field in the name subdocument, and the birth field from the matching documents:

db.bios.findOne(
   { contribs: 'OOP' },
   { _id: 0, 'name.first': 0, birth: 0 }
)