"MongoDB Learning Note 19" MongoDB Cursors and query options

MongoDB uses cursors to process the set of result documents found by the Find query;

Examples of use of cursors:

> var cursor=db.post.find ({"Name.firstname": "Joe"})    > cursor     {  "_id"  : objectid ("54ace1394ba07ed75df68f90"),  "name"  : {  " FirstName " : " Joe ", " LastName " : " Schome " }, " Age " : 28 }     {  "_id"  : objectid ("54ace753eab1d0ba4abb48ab"),  "name"  :  {  "FirstName"  :  "Joe",  "LastName"  :  "Schome"  },  "Age"  :  30 }    {  "_id"  : objectid ("54ace777eab1d0ba4abb48ac"),  " Name " : {  FirstName"  :  "Joe",  "LastName"  :  "Schome",  "comment"  : 10 },  "Age"  : 30 }    {  "_id"  :  ObjectId ("54ace781eab1d0ba4abb48ad"),  "name"  : {  "FirstName"  :  "Joe",  " LastName " : " Schome ", "Comment " : 6 }, " age " : 30 }    { " _id " :  objectid ("54ace785eab1d0ba4abb48ae"),  "name"  : {  "FirstName"  :  "Joe",   "LastName"  :  "Schome",  "comment"  : 5 },  "age"  : 30 }     {  "_id"  : objectid ("54ace789eab1d0ba4abb48af"),  "name"  :  {  "FirstName"  :  "Joe",  "LastName"  :  "Schome",  "comment"  : 7  },  "Age"  : 30 }    >

Use limit to return the first two records:

> Cursor.limit (2) {"_id": ObjectId ("54ace1394ba07ed75df68f90"), "name": {"FirstName": "Joe", "LastName": "Schom E "}," age ":--} {" _id ": ObjectId (" 54ace753eab1d0ba4abb48ab ")," name ": {" FirstName ":" Joe "," LastName ":" Schome "}," Age ": >

or skip the top 3 records using skip:

> Cursor.skip (3) {"_id": ObjectId ("54ace781eab1d0ba4abb48ad"), "name": {"FirstName": "Joe", "LastName": "Schome "," comment ": 6}," Age ": $ {" _id ": ObjectId (" 54ace785eab1d0ba4abb48ae ")," name ": {" FirstName ":" Joe "," Lastn Ame ":" Schome "," comment ": 5}," age ": + {" _id ": ObjectId (" 54ace789eab1d0ba4abb48af ")," name ": {" FirstName ": "Joe", "LastName": "Schome", "comment": 7}, "Age": >

Or use sort to specify the key value sort:

> cursor.sort ({"Age": 1})     {  "_id"  : objectid (" 54ace1394ba07ed75df68f90 "), " name " : { " FirstName " : " Joe ", " LastName "  :  "Schome"  },  "Age"  : 28 }    {  "_id"  :  objectid ("54ace753eab1d0ba4abb48ab"),  "name"  : {  "FirstName"  :  "Joe",   "LastName"  :  "Schome"  },  "Age"  : 30 }    {  " _id " : objectid (" 54ace777eab1d0ba4abb48ac "), " name " : { " FirstName " :  "Joe",  "LastName"  :  "Schome",  "comment"  : 10 },  "age"  : 30  }    {  "_id"  : objectid ("54ace781eab1d0ba4abb48ad"),  "name"  : {  "FirstName"  :  "Joe",  "LastName"  :  "Schome",  "comment"  :  6 },  "Age"  : 30 }    {  "_id"  : objectid ("54ace785eab1d0ba4abb48ae"),  "name"  : {   "FirstName"  :  "Joe",  "LastName"  :  "Schome",  "comment"  : 5 } ,  "Age"  : 30 }    {  "_id"  : objectid (" 54ace789eab1d0ba4abb48af "), " name " : { " FirstName " : " Joe ", " LastName "  :  "Schome",  "comment"  : 7 },  "age"  : 30 }

The combination of Sort/limit/skip, of course, can be adjusted in order to get different results:

> Cursor.sort ({"Name.comment": 1}). Skip (2). Limit (1) {"_id": ObjectId ("54ace785eab1d0ba4abb48ae"), "name": {" FirstName ":" Joe "," LastName ":" Schome "," comment ": 5}," Age ":}>

This article is from the "Margin with Wish" blog, please be sure to keep this source http://281816327.blog.51cto.com/907015/1600283

"MongoDB Learning Note 19" MongoDB Cursors and query options