MongoDB排序
时间：2020-02-23 14:40:52 来源:igfitidea点击:
MongoDB排序方法按用户在输入参数中指定的升序或者降序对文档进行排序。
MongoDB排序
MongoDB排序方法的语法为：
{ $sort:{<field1>:<sort order>........}}
排序顺序可以采用以下值：
1：指定字段应按升序排序
-1：指定字段应按降序排序
MongoDB排序示例
让我们看一个对字段排序的例子。
请注意，您可以使用MongoDB插入来创建示例数据。
>db.car.find().sort({speed:-1})
{ "_id" : ObjectId("5471d72e0ce70a7026ebefee"), "name" : "Esteem", "color" : "JetRed", "cno" : "H414", "mfdcountry" : "Italy", "speed" : 65 }
{ "_id" : 3, "name" : "Alto", "color" : "Silver", "cno" : "H413", "mfdcountry" : "San Franceco", "speed" : 55 }
{ "_id" : 2, "name" : "Volkswagen", "color" : "Blue", "cno" : "H412", "mfdcountry" : "Japan", "speed" : 52 }
{ "_id" : 1, "name" : "Polo", "color" : "White", "cno" : "H411", "mfdcountry" : "Germany", "speed" : 45 }
按速度字段的降序对收车文档进行排序。
>db.car.find().sort({name:1})
{ "_id" : 3, "name" : "Alto", "color" : "Silver", "cno" : "H413", "mfdcountry" : "San Franceco", "speed" : 55 }
{ "_id" : ObjectId("5471d72e0ce70a7026ebefee"), "name" : "Esteem", "color" : "JetRed", "cno" : "H414", "mfdcountry" : "Italy", "speed" : 65 }
{ "_id" : 1, "name" : "Polo", "color" : "White", "cno" : "H411", "mfdcountry" : "Germany", "speed" : 45 }
{ "_id" : 2, "name" : "Volkswagen", "color" : "Blue", "cno" : "H412", "mfdcountry" : "Japan", "speed" : 52 }
您会注意到，这会在名称字段上按升序对收车文件进行排序。
>db.car.find().sort({speed:-1,name:1})
{ "_id" : ObjectId("54729a20ab36ed23e31c68f1"), "name" : "Audi", "color" : "Grey", "cno" : "H415", "mfdcountry" : "Rome", "speed" : 65 }
{ "_id" : ObjectId("5471d72e0ce70a7026ebefee"), "name" : "Esteem", "color" : "JetRed", "cno" : "H414", "mfdcountry" : "Italy", "speed" : 65 }
{ "_id" : ObjectId("5472988cab36ed23e31c68f0"), "name" : "skoda", "color" : "JetRed", "cno" : "H415", "mfdcountry" : "Chez", "speed" : 65 }
{ "_id" : 3, "name" : "Alto", "color" : "Silver", "cno" : "H413", "mfdcountry" : "San Franceco", "speed" : 55 }
{ "_id" : 2, "name" : "Volkswagen", "color" : "Blue", "cno" : "H412", "mfdcountry" : "Japan", "speed" : 52 }
{ "_id" : 1, "name" : "Polo", "color" : "White", "cno" : "H411", "mfdcountry" : "Germany", "speed" : 45 }
上面的示例基于速度对汽车集合进行降序排序，然后对具有相同速度的汽车按名称进行升序排序(65)。
限制MongoDB排序操作的结果
如果排序操作超过32兆字节，则MongoDB返回错误。
为了消除此错误，可以将索引与limit方法结合使用。
限制结果是要返回的32兆字节以内的文档数。
例如;
>db.car.find().sort( {speed:-1,name:1 }).limit(10)
此MongoDB排序操作将返回的文档数限制为10，并确保该数量在32 MB的范围内。
可以如下所示创建索引。
>db.car.ensureIndex({ name:1,speed:-1})
{
"createdCollectionAutomatically" : false,
"numIndexesBefore" : 2,
"numIndexesAfter" : 3,
"ok" : 1
}
这样可以确保为汽车集合创建索引。
我们也可以使用Mongo shell的createIndex()方法。
指定投影字段
当用户指定要投影和排序的字段时，MongoDB引擎将首先对生成的文档进行排序。
例如;
>db.car.find({speed: { $gt:14}},{name:1,speed:1}).sort({"speed":-1})
{ "_id" : 11, "name" : "Polo", "speed" : 45 }
{ "_id" : 10, "name" : "Volkswagen", "speed" : 44 }
{ "_id" : 9, "name" : "Skoda", "speed" : 43 }
{ "_id" : 12, "name" : "Ecosport", "speed" : 15 }
此操作首先按速度降序对汽车进行排序，然后在结果文档中仅显示id，名称和速度字段。
MongoDB排序的自然顺序
$natural参数按数据库中存在的顺序返回所有文档。
该顺序基本上描述了记录的插入顺序，但由于更新或者删除操作而导致文档重新定位的情况除外。
例如;
>db.car.find().sort( { $natural: 1 })
{ "_id" : 9, "name" : "Skoda", "color" : "Red", "cno" : "H622", "mfdcountry" : "Chez", "speed" : 43 }
{ "_id" : 10, "name" : "Volkswagen", "color" : "Blue", "cno" : "H623", "mfdcountry" : "Germany", "speed" : 44 }
{ "_id" : 11, "name" : "Polo", "color" : "White", "cno" : "H624", "mfdcountry" : "Japan", "speed" : 45 }
{ "_id" : 12, "name" : "Ecosport", "color" : "NavyBlue", "cno" : "H625", "mfdcountry" : "Japan", "speed" : 15 }
按照将文档插入数据库的顺序来检索文档。
MongoDB排序Java程序
在本节中，我们将研究一个Java程序以升序和降序执行排序操作。
以下是针对Java驱动程序版本2.x的MongoDB排序程序。
package com.theitroad.mongodb;
import java.net.UnknownHostException;
import java.util.List;
import com.mongodb.BasicDBObject;
import com.mongodb.DB;
import com.mongodb.DBCollection;
import com.mongodb.DBCursor;
import com.mongodb.DBObject;
import com.mongodb.MongoClient;
public class MongoDBSort {
//method for sorting in ascending order based on name
public static void sortAscending() throws UnknownHostException {
//Get a new connection to the db assuming that it is running
MongoClient m1 = new MongoClient("localhost");
//use test as a datbase,use your database here
DB d1 = m1.getDB("test");
//fetch the collection object ,car is used here,use your own
DBCollection coll = d1.getCollection("car");
//find method is called and result stored in cursor
DBCursor car = coll.find();
//sorting the cursor based in ascending order based on name field
car.sort(new BasicDBObject("name", 1));
//iterating throug cursor and printing all the documents stored in
//cursor
try {
while (car.hasNext()) {
System.out.println(car.next());
}
} finally {
car.close();
}
}
//method for sorting in descending order based on speed
public static void sortDescending() throws UnknownHostException {
MongoClient m1 = new MongoClient("localhost");
DB d1 = m1.getDB("test");
DBCollection coll = d1.getCollection("car");
DBCursor car = coll.find();
//sorting the cursor based in descending order based on speed field
car.sort(new BasicDBObject("speed", -1));
System.out
.println("Sorts in Descending order-------------------------------------------");
try {
while (car.hasNext()) {
System.out.println(car.next());
}
} finally {
car.close();
}
}
//method for sorting in descending order based on speed and ascending order
//based on name
public static void sortDescendingAscending() throws UnknownHostException {
MongoClient m1 = new MongoClient("localhost");
DB d1 = m1.getDB("test");
DBCollection coll = d1.getCollection("car");
DBCursor car = coll.find();
//sort speed in descending order then name in ascending order
car.sort(new BasicDBObject("speed", -1).append("name", 1));
System.out
.println("Combining two fields to sort in ascending and descending orders-----------------");
try {
while (car.hasNext()) {
System.out.println(car.next());
}
} finally {
car.close();
}
}
public static void sortlimit() throws UnknownHostException {
MongoClient m1 = new MongoClient("localhost");
DB d1 = m1.getDB("test");
DBCollection coll = d1.getCollection("car");
DBObject q1 = new BasicDBObject("speed", new BasicDBObject("$gt", 15));
BasicDBObject fields = new BasicDBObject("name", 1).append("speed", 1);
//find method is called and result stored //fetch the collection object
//,car is used here,use your ownin cursor
DBCursor car = coll.find(q1, fields);
//sorting the cursor based in ascending order based on name field
car.sort(new BasicDBObject("name", -1)).limit(2);
System.out.println("limit--------------------------");
//iterating throug cursor and printing all the documents stored in
//cursor
try {
while (car.hasNext()) {
System.out.println(car.next());
}
} finally {
car.close();
}
}
public static void sortProjectionfields() throws UnknownHostException {
MongoClient m1 = new MongoClient("localhost");
DB db = m1.getDB("test");
DBCollection col = db.getCollection("car");
DBObject query = new BasicDBObject("speed",
new BasicDBObject("$gt", 40));
//fields with name and speed field is specified and only these fields
//are displayed
BasicDBObject fields = new BasicDBObject("name", 1).append("speed", 1);
DBCursor carCursor1 = col.find(query, fields);
System.out
.println("------------------------------------------------------");
try {
while (carCursor1.hasNext()) {
System.out.println(carCursor1.next());
}
} finally {
carCursor1.close();
}
}
public static void sortnaturalordering() throws UnknownHostException {
MongoClient m1 = new MongoClient("localhost");
DB d1 = m1.getDB("test");
DBCollection coll = d1.getCollection("car");
DBObject q1 = new BasicDBObject("speed", new BasicDBObject("$gt", 15));
BasicDBObject fields = new BasicDBObject("name", 1).append("speed", 1);
//find method is called and result stored
//fetch the collection object ,car is used here,use your own cursor
DBCursor car = coll.find(q1, fields);
//sorting the cursor based in ascending order based on name field
car.sort(new BasicDBObject("$natural", -1));
System.out.println("natural ordering---------------");
//iterating through cursor and printing all the documents stored in
//cursor
try {
while (car.hasNext()) {
System.out.println(car.next());
}
} finally {
car.close();
}
}
public static void createIndex(String on, int type)
throws UnknownHostException {
MongoClient m1 = new MongoClient("localhost");
DB d1 = m1.getDB("test");
DBCollection coll = d1.getCollection("car");
coll.createIndex(new BasicDBObject(on, type));
System.out.println("created index---------------------");
List<DBObject> list = coll.getIndexInfo();
for (DBObject o : list) {
System.out.println(o);
}
}
public static void main(String[] args) throws UnknownHostException {
//invoking methods for performing sorting
sortAscending();
sortDescending();
sortDescendingAscending();
sortlimit();
sortProjectionfields();
sortnaturalordering();
createIndex("name", 1);
}
}
上面的程序导致以下输出。
{ "_id" : 3.0 , "name" : "Alto" , "color" : "Silver" , "cno" : "H413" , "mfdcountry" : "San Franceco" , "speed" : 55.0}
{ "_id" : { "$oid" : "5471d72e0ce70a7026ebefee"} , "name" : "Esteem" , "color" : "JetRed" , "cno" : "H414" , "mfdcountry" : "Italy" , "speed" : 65.0}
{ "_id" : 1.0 , "name" : "Polo" , "color" : "White" , "cno" : "H411" , "mfdcountry" : "Germany" , "speed" : 45.0}
{ "_id" : 2.0 , "name" : "Volkswagen" , "color" : "Blue" , "cno" : "H412" , "mfdcountry" : "Japan" , "speed" : 52.0}
Sorting in Descending order------------------------------------------
{ "_id" : { "$oid" : "5471d72e0ce70a7026ebefee"} , "name" : "Esteem" , "color" : "JetRed" , "cno" : "H414" , "mfdcountry" : "Italy" , "speed" : 65.0}
{ "_id" : 3.0 , "name" : "Alto" , "color" : "Silver" , "cno" : "H413" , "mfdcountry" : "San Franceco" , "speed" : 55.0}
{ "_id" : 2.0 , "name" : "Volkswagen" , "color" : "Blue" , "cno" : "H412" , "mfdcountry" : "Japan" , "speed" : 52.0}
{ "_id" : 1.0 , "name" : "Polo" , "color" : "White" , "cno" : "H411" , "mfdcountry" : "Germany" , "speed" : 45.0}
sorting ascending descending----------------
{ "_id" : { "$oid" : "54729a20ab36ed23e31c68f1"} , "name" : "Audi" , "color" : "Grey" , "cno" : "H415" , "mfdcountry" : "Rome" , "speed" : 65.0}
{ "_id" : { "$oid" : "5471d72e0ce70a7026ebefee"} , "name" : "Esteem" , "color" : "JetRed" , "cno" : "H414" , "mfdcountry" : "Italy" , "speed" : 65.0}
{ "_id" : { "$oid" : "5472988cab36ed23e31c68f0"} , "name" : "skoda" , "color" : "JetRed" , "cno" : "H415" , "mfdcountry" : "Chez" , "speed" : 65.0}
{ "_id" : 3.0 , "name" : "Alto" , "color" : "Silver" , "cno" : "H413" , "mfdcountry" : "San Franceco" , "speed" : 55.0}
{ "_id" : 2.0 , "name" : "Volkswagen" , "color" : "Blue" , "cno" : "H412" , "mfdcountry" : "Japan" , "speed" : 52.0}
{ "_id" : 1.0 , "name" : "Polo" , "color" : "White" , "cno" : "H411" , "mfdcountry" : "Germany" , "speed" : 45.0}
limit-------------------------
{ "_id" : 10.0 , "name" : "Volkswagen" , "speed" : 44.0}
{ "_id" : 9.0 , "name" : "Skoda" , "speed" : 43.0}
-----------------------------------------------------
{ "_id" : 11.0 , "name" : "Polo" , "speed" : 45.0}
{ "_id" : 10.0 , "name" : "Volkswagen" , "speed" : 44.0}
{ "_id" : 9.0 , "name" : "Skoda" , "speed" : 43.0}
natural ordering--------------
{ "_id" : 11.0 , "name" : "Polo" , "speed" : 45.0}
{ "_id" : 10.0 , "name" : "Volkswagen" , "speed" : 44.0}
{ "_id" : 9.0 , "name" : "Skoda" , "speed" : 43.0}
created index--------------------
{ "v" : 1 , "key" : { "_id" : 1} , "name" : "_id_" , "ns" : "test.car"}
{ "v" : 1 , "key" : { "speed" : -1.0 , "name" : 1.0} , "name" : "speed_-1_name_1" , "ns" : "test.car"}
{ "v" : 1 , "key" : { "name" : 1.0 , "speed" : -1.0} , "name" : "name_1_speed_-1" , "ns" : "test.car"}
{ "v" : 1 , "key" : { "name" : 1} , "name" : "name_1" , "ns" : "test.car"}
如果您使用的是MongoDB Java驱动程序版本3.x，则以下代码应可用。
已通过3.5.0版进行测试
package com.theitroad.mongodb.main;
import java.net.UnknownHostException;
import java.util.List;
import org.bson.Document;
import com.mongodb.BasicDBObject;
import com.mongodb.DB;
import com.mongodb.DBCollection;
import com.mongodb.DBCursor;
import com.mongodb.DBObject;
import com.mongodb.MongoClient;
import com.mongodb.client.FindIterable;
import com.mongodb.client.MongoCollection;
import com.mongodb.client.MongoCursor;
import com.mongodb.client.MongoDatabase;
public class MongoDBSort {
//method for sorting in ascending order based on name
public static void sortAscending() throws UnknownHostException {
//Get a new connection to the db assuming that it is running
MongoClient mc = new MongoClient("localhost");
//use test as a datbase,use your database here
MongoDatabase db = mc.getDatabase("theitroad");
//fetch the collection object ,car is used here,use your own
MongoCollection<Document> coll = db.getCollection("car");
//find method is called and result stored in cursor
FindIterable<Document> car = coll.find();
//sorting the cursor based in ascending order based on name field
car.sort(new BasicDBObject("name", 1));
//iterating through cursor and printing all the documents stored in cursor
MongoCursor<Document> iterator = car.iterator();
try {
while (iterator.hasNext()) {
System.out.println(iterator.next());
}
} finally {
iterator.close();
mc.close();
}
}
//method for sorting in descending order based on speed
public static void sortDescending() throws UnknownHostException {
MongoClient mc = new MongoClient("localhost");
MongoDatabase db = mc.getDatabase("test");
MongoCollection<Document> coll = db.getCollection("car");
FindIterable<Document> car = coll.find();
//sorting the cursor based in descending order based on speed field
car.sort(new BasicDBObject("speed", -1));
System.out.println("Sorts in Descending order");
MongoCursor<Document> iterator = car.iterator();
try {
while (iterator.hasNext()) {
System.out.println(iterator.next());
}
} finally {
iterator.close();
mc.close();
}
}
//method for sorting in descending order based on speed and ascending order
//based on name
public static void sortDescendingAscending() throws UnknownHostException {
MongoClient mc = new MongoClient("localhost");
MongoDatabase db = mc.getDatabase("test");
MongoCollection<Document> coll = db.getCollection("car");
FindIterable<Document> car = coll.find();
//sort speed in descending order then name in ascending order
car.sort(new BasicDBObject("speed", -1).append("name", 1));
System.out.println("Combining two fields to sort in ascending and descending orders");
MongoCursor<Document> iterator = car.iterator();
try {
while (iterator.hasNext()) {
System.out.println(iterator.next());
}
} finally {
iterator.close();
mc.close();
}
}
public static void sortlimit() throws UnknownHostException {
MongoClient mc = new MongoClient("localhost");
MongoDatabase db = mc.getDatabase("test");
MongoCollection<Document> coll = db.getCollection("car");
BasicDBObject q1 = new BasicDBObject("speed", new BasicDBObject("$gt", 15));
//find method is called and result stored //fetch the collection object
//,car is used here,use your ownin cursor
FindIterable<Document> car = coll.find(q1);
//sorting the cursor based in ascending order based on name field
car.sort(new BasicDBObject("name", -1)).limit(2);
System.out.println("limit example");
//iterating through cursor and printing all the documents stored in
//cursor
MongoCursor<Document> iterator = car.iterator();
try {
while (iterator.hasNext()) {
System.out.println(iterator.next());
}
} finally {
iterator.close();
mc.close();
}
}
public static void sortProjectionfields() throws UnknownHostException {
MongoClient mc = new MongoClient("localhost");
MongoDatabase db = mc.getDatabase("test");
MongoCollection<Document> col = db.getCollection("car");
BasicDBObject query = new BasicDBObject("speed",
new BasicDBObject("$gt", 40));
FindIterable<Document> carCursor1 = col.find(query);
System.out.println("------------------------------------------------------");
MongoCursor<Document> iterator = carCursor1.iterator();
try {
while (iterator.hasNext()) {
System.out.println(iterator.next());
}
} finally {
iterator.close();
mc.close();
}
}
public static void sortnaturalordering() throws UnknownHostException {
MongoClient mc = new MongoClient("localhost");
MongoDatabase db = mc.getDatabase("test");
MongoCollection<Document> coll = db.getCollection("car");
BasicDBObject q1 = new BasicDBObject("speed", new BasicDBObject("$gt", 15));
BasicDBObject fields = new BasicDBObject("name", 1).append("speed", 1);
//find method is called and result stored
//fetch the collection object ,car is used here,use your own cursor
FindIterable<Document> car = coll.find(q1);
//sorting the cursor based in ascending order based on name field
car.sort(new BasicDBObject("$natural", -1));
System.out.println("natural ordering---------------");
//iterating through cursor and printing all the documents stored in
//cursor
MongoCursor<Document> iterator = car.iterator();
try {
while (iterator.hasNext()) {
System.out.println(iterator.next());
}
} finally {
iterator.close();
mc.close();
}
}
public static void createIndex(String on, int type)
throws UnknownHostException {
MongoClient mc = new MongoClient("localhost");
MongoDatabase db = mc.getDatabase("test");
MongoCollection<Document> coll = db.getCollection("car");
String indexName = coll.createIndex(new BasicDBObject(on, type));
System.out.println("created index name="+indexName);
MongoCursor<Document> iterator = coll.listIndexes().iterator();
try {
while (iterator.hasNext()) {
System.out.println(iterator.next());
}
} finally {
iterator.close();
mc.close();
}
}
public static void main(String[] args) throws UnknownHostException {
//invoking methods for performing sorting
sortAscending();
sortDescending();
sortDescendingAscending();
sortlimit();
sortProjectionfields();
sortnaturalordering();
createIndex("name", 1);
}
}
