MongoDB数据查询方法干货篇(2)-木庄网络博客

下面将会查询不存在sex这一项的信息

db.user.find({sex:{$exists:false}})
//结果
{ "_id" : ObjectId("59058460fe58ed1089f2a5cd"), "name" : "xiaoming", "age" : 33, "tags" : [ "python", "java" ], "grades" : [ 66, 22, 44, 88 ], "school" : { "name" : "kuangda", "city" : "xuzhou" } }
db.user.find({sex:{$exists:true}});
//结果
{ "_id" : ObjectId("59058460fe58ed1089f2a5cb"), "name" : "jack", "age" : 22, "sex" : "Man", "tags" : [ "python", "c++", "c" ], "grades" : [ 22, 33, 44, 55 ], "school" : { "name" : "shida", "city" : "xuzhou" } }
{ "_id" : ObjectId("59058460fe58ed1089f2a5cc"), "name" : "jhon", "age" : 33, "sex" : null, "tags" : [ "python", "java" ], "grades" : [ 66, 22, 44, 88 ], "school" : { "name" : "kuangda", "city" : "xuzhou" } }

$or

执行逻辑OR运算,指定一个至少包含两个表达式的数组，选择出至少满足数组中一条表达式的文档。

语法： { $or: [ { <expression1> }, { <expression2> }, ... , { <expressionN> } ] }

下面将要查找age等于22或者age等于33的值

db.user.find({$or:[{age:22},{age:33}]})
//结果
{ "_id" : ObjectId("59058460fe58ed1089f2a5cb"), "name" : "jack", "age" : 22, "sex" : "Man", "tags" : [ "python", "c++", "c" ], "grades" : [ 22, 33, 44, 55 ], "school" : { "name" : "shida", "city" : "xuzhou" } }
{ "_id" : ObjectId("59058460fe58ed1089f2a5cc"), "name" : "jhon", "age" : 33, "sex" : null, "tags" : [ "python", "java" ], "grades" : [ 66, 22, 44, 88 ], "school" : { "name" : "kuangda", "city" : "xuzhou" } }
{ "_id" : ObjectId("59058460fe58ed1089f2a5cd"), "name" : "xiaoming", "age" : 33, "tags" : [ "python", "java" ], "grades" : [ 66, 22, 44, 88 ], "school" : { "name" : "kuangda", "city" : "xuzhou" } }

下面将会查找出年龄为22或者33并且姓名为jack的人的信息

db.user.find({name:'jack',$or:[{age:33},{age:22}]})
//结果
{ "_id" : ObjectId("59058460fe58ed1089f2a5cb"), "name" : "jack", "age" : 22, "sex" : "Man", "tags" : [ "python", "c++", "c" ], "grades" : [ 22, 33, 44, 55 ], "school" : { "name" : "shida", "city" : "xuzhou" } }

$and

指定一个至少包含两个表达式的数组，选择出满足该数组中所有表达式的文档。$and操作符使用短路操作，若第一个表达式的值为“false”,余下的表达式将不会执行。

语法： { $and: [ { <expression1> }, { <expression2> } , ... , { <expressionN> } ] }

下面将会查找年龄在20-30之间的信息，对于下面使用逗号分隔符的表达式列表，MongoDB会提供一个隐式的$and操作：

db.user.find({$and:[{age:{$gt:20}},{age:{$lt:30}}]})
//上述语句相当于db.user.find({age:{$gt:20},age:{$lt:30}})
//结果
{ "_id" : ObjectId("59058460fe58ed1089f2a5cb"), "name" : "jack", "age" : 22, "sex" : "Man", "tags" : [ "python", "c++", "c" ], "grades" : [ 22, 33, 44, 55 ], "school" : { "name" : "shida", "city" : "xuzhou" } }

$in

匹配键值等于指定数组中任意值的文档。类似sql中in，只要匹配一个value就会输出

语法： { field: { $in: [<value1>, <value2>, ... <valueN> ] } }

下面将会查找grades中存在22,33之间的任意一个数的信息

 db.user.find({grades:{$in:[22,33]}})
 
 //输出
 
{ "_id" : ObjectId("59058460fe58ed1089f2a5cb"), "name" : "jack", "age" : 22, "sex" : "Man", "tags" : [ "python", "c++", "c" ], "grades" : [ 22, 33, 44, 55 ], "school" : { "name" : "shida", "city" : "xuzhou" } }
{ "_id" : ObjectId("59058460fe58ed1089f2a5cc"), "name" : "jhon", "age" : 33, "sex" : null, "tags" : [ "python", "java" ], "grades" : [ 66, 22, 44, 88 ], "school" : { "name" : "kuangda", "city" : "xuzhou" } }
{ "_id" : ObjectId("59058460fe58ed1089f2a5cd"), "name" : "xiaoming", "age" : 33, "tags" : [ "python", "java" ], "grades" : [ 66, 22, 44, 88 ], "school" : { "name" : "kuangda", "city" : "xuzhou" } }

$nin

匹配键不存在或者键值不等于指定数组的任意值的文档。类似sql中not in(SQL中字段不存在使用会有语法错误).

查询出grades中不存在100或者44的文档

db.user.find({grades:{$nin:[100,44]}})

$not

执行逻辑NOT运算，选择出不能匹配表达式的文档，包括没有指定键的文档。$not操作符不能独立使用，必须跟其他操作一起使用

语法: { field: { $not: { } } }

查询年龄不大于30的信息

db.user.find({age:{$not:{$gt:30}}})
//输出
{ "_id" : ObjectId("59058460fe58ed1089f2a5cb"), "name" : "jack", "age" : 22, "sex" : "Man", "tags" : [ "python", "c++", "c" ], "grades" : [ 22, 33, 44, 55 ], "school" : { "name" : "shida", "city" : "xuzhou" } }

迭代游标的查询

学过高级语言的朋友都知道迭代的问题，像java,下面使用迭代的方法查询

var cursor=db.usr.find();
//这里使用迭代输出所有的数据
while(cursor.hasNext()) //这里的hasNext()是判断是否下一个中还有可迭代的值，如果没有返回false
{
 printjson(cursor.next()); //这里的cursor.next是迭代的输出，printjson是代替print(tojson()) 
}
print cursor.count() //输出其中有多少个数据
cursor.forEach(printjson); //forEach输出
var document=cursor.toArray(); //将迭代对象转换成数组
print document[0]; //以数组的形式输出

总结

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标签：MongoDB

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