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- $showDiskLoc
$showDiskLoc¶
- $showDiskLoc¶
$showDiskLoc option adds a field $diskLoc to the returned documents. The value of the added $diskLoc field is a document that contains the disk location information:
"$diskLoc": { "file": <int>, "offset": <int> }
The mongo shell provides the cursor.showDiskLoc() method for $showDiskLoc:
db.collection.find().showDiskLoc()
You can also specify the $showDiskLoc option in either of the following forms:
db.collection.find( { <query> } )._addSpecial("$showDiskLoc" , true) db.collection.find( { $query: { <query> }, $showDiskLoc: true } )
Example¶
The following operation appends the showDiskLoc() method to the db.collection.find() method in order to include in the matching documents the disk location information:
db.collection.find( { a: 1 } ).showDiskLoc()
The operation returns the following documents, which includes the $diskLoc field:
{
"_id" : ObjectId("53908ccb18facd50a75bfbac"),
"a" : 1,
"b" : 1,
"$diskLoc" : { "file" : 0, "offset" : 16195760 }
}
{
"_id" : ObjectId("53908cd518facd50a75bfbad"),
"a" : 1,
"b" : 2,
"$diskLoc" : { "file" : 0, "offset" : 16195824 }
}
The projection can also access the added field $diskLoc, as in the following example:
db.collection.find( { a: 1 }, { $diskLoc: 1 } ).showDiskLoc()
The operation returns just the _id field and the $diskLoc field in the matching documents:
{
"_id" : ObjectId("53908ccb18facd50a75bfbac"),
"$diskLoc" : { "file" : 0, "offset" : 16195760 }
}
{
"_id" : ObjectId("53908cd518facd50a75bfbad"),
"$diskLoc" : { "file" : 0, "offset" : 16195824 }
}