find()
- MongoDB 中查询文档使用 find()
- find() 方法以非结构化的方式来显示所要查询的文档
语法格式
db.collection.find(query, projection)
- query：可选项，设置查询操作符指定查询条件
- projection ：可选项，指定要在与 query 匹配的文档中返回的字段，如果忽略此选项则返回所有字段
pretty()
为了查看文档的格式更加直观美丽，可以最后加个 pretty() 方法
db.inventory.find().pretty()
{
"_id" : ObjectId("60b5e622dd6e93ee8bf35a9d"),
"item" : "journal",
"qty" : 25,
"size" : {
"h" : 14,
"w" : 21,
"uom" : "cm"
},
"status" : "A"
}
注意：findOne() 是没有的跟 pretty() 方法的
findOne()
和 find() 的都是查询文档，但是只返回匹配查询条件成功的第一个文档
语法格式
db.collection.findOne(query, projection)
查询条件
MongoDB 支持查询条件操作符，下表为 MongoDB 与 RDBMS（关系型数据库，Mysql）常见的查询条件操作符的对比
| 操作符 | 格式 | 实例 | 与 RDBMS where 语句比较 |
|---|---|---|---|
| 等于（=） | {<key> : {<value>}} | db.test.find( {price : 24} ) | where price = 24 |
| 大于（>） | {<key> : {$gt : <value>}} | db.test.find( {price : {$gt : 24}} ) | where price > 24 |
| 小于（<） | {<key> : {$lt : <value>}} | db.test.find( {price : {$lt : 24}} ) | where price < 24 |
| 大于等于（>=） | {<key> : {$gte : <value>}} | db.test.find( {price : {$gte : 24}} ) | where price >= 24 |
| 小于等于（<=） | {<key> : {$lte : <value>}} | db.test.find( {price : {$lte : 24}} ) | where price <= 24 |
| 不等于（!=） | {<key> : {$ne : <value>}} | db.test.find( {price : {$ne : 24}} ) | where price != 24 |
| 与（and） | {key01 : value01, key02 : value02, ...} | db.test.find( {name : "小菠萝测试笔记", price : 24} ) | where name = "小菠萝测试笔记" and price = 24 |
| 或（or） | {$or : [{key01 : value01}, {key02 : value02}, ...]} | db.test.find( {$or:[{name : "小菠萝测试笔记"},{price : 24}]7} ) | where name = "小菠萝测试笔记" or price = 24 |
| in | {<key> : {$in : [a,b,c,d.....]}} |
db.test.find( { qty: { $in: [ 5, 15 ] } } ) |
where qty in (5,15) |
| not in | {<key> : {$nin : [a,b,c,d.....]}} | db.test.find( { qty: { $nin: [ 5, 15 ] } } ) | where qty not in (5,15) |
插入测试数据
db.inventory.insertMany([
{ item: "journal", qty: 25, size: { h: 14, w: 21, uom: "cm" }, status: "A" },
{ item: "notebook", qty: 50, size: { h: 8.5, w: 11, uom: "in" }, status: "A" },
{ item: "paper", qty: 100, size: { h: 8.5, w: 11, uom: "in" }, status: "D" },
{ item: "planner", qty: 75, size: { h: 22.85, w: 30, uom: "cm" }, status: "D" },
{ item: "postcard", qty: 45, size: { h: 10, w: 15.25, uom: "cm" }, status: "A" }
]);
后面所有栗子都是以这些数据为准
查询所有文档
> db.inventory.find( {} )
{ "_id" : ObjectId("60b5e622dd6e93ee8bf35a9d"), "item" : "journal", "qty" : 25, "size" : { "h" : 14, "w" : 21, "uom" : "cm" }, "status" : "A" }
{ "_id" : ObjectId("60b5e622dd6e93ee8bf35a9e"), "item" : "notebook", "qty" : 50, "size" : { "h" : 8.5, "w" : 11, "uom" : "in" }, "status" : "A" }
{ "_id" : ObjectId("60b5e622dd6e93ee8bf35a9f"), "item" : "paper", "qty" : 100, "size" : { "h" : 8.5, "w" : 11, "uom" : "in" }, "status" : "D" }
{ "_id" : ObjectId("60b5e622dd6e93ee8bf35aa0"), "item" : "planner", "qty" : 75, "size" : { "h" : 22.85, "w" : 30, "uom" : "cm" }, "status" : "D" }
{ "_id" : ObjectId("60b5e622dd6e93ee8bf35aa1"), "item" : "postcard", "qty" : 45, "size" : { "h" : 10, "w" : 15.25, "uom" : "cm" }, "status" : "A" }
等价 Mysql 的写法
SELECT * FROM inventory
查询文档，= 等于操作
语法格式
{ <field1>: <value1>}
实际栗子
> db.inventory.find( { status: "D" } )
{ "_id" : ObjectId("60b5e622dd6e93ee8bf35a9f"), "item" : "paper", "qty" : 100, "size" : { "h" : 8.5, "w" : 11, "uom" : "in" }, "status" : "D" }
{ "_id" : ObjectId("60b5e622dd6e93ee8bf35aa0"), "item" : "planner", "qty" : 75, "size" : { "h" : 22.85, "w" : 30, "uom" : "cm" }, "status" : "D" }
等价 Mysql 的写法
SELECT * FROM inventory WHERE status = "D"
查询操作符
这里有一个概念叫查询操作符，其实就是上面查询条件列的那些栗子
使用查询操作符的语法格式
{ <field1>: { <operator1>: <value1> }, ... }
还有哪些查询操作符后面再展开详解
查询文档，and 与操作
> db.inventory.find( { status: "A", qty: { $lt: 30 } } )
{ "_id" : ObjectId("60b5e622dd6e93ee8bf35a9d"), "item" : "journal", "qty" : 25, "size" : { "h" : 14, "w" : 21, "uom" : "cm" }, "status" : "A" }
等价 Mysql 的写法
SELECT * FROM inventory WHERE status = "A" AND qty < 30
查询文档，in 操作
> db.inventory.find( { status: { $in: [ "A", "D" ] } } )
{ "_id" : ObjectId("60b5e622dd6e93ee8bf35a9d"), "item" : "journal", "qty" : 25, "size" : { "h" : 14, "w" : 21, "uom" : "cm" }, "status" : "A" }
{ "_id" : ObjectId("60b5e622dd6e93ee8bf35a9e"), "item" : "notebook", "qty" : 50, "size" : { "h" : 8.5, "w" : 11, "uom" : "in" }, "status" : "A" }
{ "_id" : ObjectId("60b5e622dd6e93ee8bf35a9f"), "item" : "paper", "qty" : 100, "size" : { "h" : 8.5, "w" : 11, "uom" : "in" }, "status" : "D" }
{ "_id" : ObjectId("60b5e622dd6e93ee8bf35aa0"), "item" : "planner", "qty" : 75, "size" : { "h" : 22.85, "w" : 30, "uom" : "cm" }, "status" : "D" }
{ "_id" : ObjectId("60b5e622dd6e93ee8bf35aa1"), "item" : "postcard", "qty" : 45, "size" : { "h" : 10, "w" : 15.25, "uom" : "cm" }, "status" : "A" }
等价 Mysql 的写法
SELECT * FROM inventory WHERE status in ("A", "D")
查询文档，or 或操作
> db.inventory.find({$or:[{status:"A"},{qty:{$gt:50}}]})
{ "_id" : ObjectId("60b5e622dd6e93ee8bf35a9d"), "item" : "journal", "qty" : 25, "size" : { "h" : 14, "w" : 21, "uom" : "cm" }, "status" : "A" }
{ "_id" : ObjectId("60b5e622dd6e93ee8bf35a9e"), "item" : "notebook", "qty" : 50, "size" : { "h" : 8.5, "w" : 11, "uom" : "in" }, "status" : "A" }
{ "_id" : ObjectId("60b5e622dd6e93ee8bf35a9f"), "item" : "paper", "qty" : 100, "size" : { "h" : 8.5, "w" : 11, "uom" : "in" }, "status" : "D" }
{ "_id" : ObjectId("60b5e622dd6e93ee8bf35aa0"), "item" : "planner", "qty" : 75, "size" : { "h" : 22.85, "w" : 30, "uom" : "cm" }, "status" : "D" }
{ "_id" : ObjectId("60b5e622dd6e93ee8bf35aa1"), "item" : "postcard", "qty" : 45, "size" : { "h" : 10, "w" : 15.25, "uom" : "cm" }, "status" : "A" }
等价 Mysql 的写法
SELECT * FROM inventory WHERE status = "A" OR qty > 50
查询文档，and 加 or 的操作
查询文档选择集合中 status 为“A”、qty小于（$lt）30或 item 以字符 p 开头的所有文档
db.inventory.find( {
status: "A",
$or: [ { qty: { $lt: 30 } }, { item: /^p/ } ]
} )
MongoDB 支持正则表达式
等价 Mysql 的写法
SELECT * FROM inventory WHERE status = "A" AND ( qty < 30 OR item LIKE "p%")