https://docs.MongoDB.com/manual/reference/method/db.collection.find/
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查询文档
db.collection.find(query, projection)
方法：
db.collection.find()
Additional Methods
db.collection.findOne
In aggregation pipeline, the $match pipeline stage provides access to MongoDB queries.
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" }
]);
参考：
> db.inventory.find( {} ,{_id:0})
重庆分公司
重庆分公司
{ "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" }操作必须以键值对的方式，必须用{}括起来，所以所有的查询先用{}括起来
1、Select All Documents in a Collection
db.inventory.find( {} )=db.inventory.find()
2、Specify Equality Condition
db.inventory.find( { status: "D" } )
SELECT * FROM inventory WHERE status = "D"
{ "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" }3、Specify Conditions Using Query Operators
db.inventory.find( { status: { $in: [ "A", "D" ] } } )
SELECT * FROM inventory WHERE status in ("A", "D")
{ "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" }4、Specify AND Conditions
db.inventory.find( { status: "A", qty: { $lt: 30 } } )
SELECT * FROM inventory WHERE status = "A" AND qty < 30
{ "item" : "journal", "qty" : 25, "size" : { "h" : 14, "w" : 21, "uom" : "cm" }, "status" : "A" }5、Specify OR Conditions
db.inventory.find( { $or: [ { status: "A" }, { qty: { $lt: 30 } } ] } )
SELECT * FROM inventory WHERE status = "A" OR qty < 30
{ "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" : "postcard", "qty" : 45, "size" : { "h" : 10, "w" : 15.25, "uom" : "cm" }, "status" : "A" }6、Specify AND as well as OR Conditions
db.inventory.find( {
status: "A",
$or: [ { qty: { $lt: 30 } }, { item: /^p/ } ]
} )
SELECT * FROM inventory WHERE status = "A" AND ( qty < 30 OR item LIKE "p%")
{ "item" : "journal", "qty" : 25, "size" : { "h" : 14, "w" : 21, "uom" : "cm" }, "status" : "A" }
{ "item" : "postcard", "qty" : 45, "size" : { "h" : 10, "w" : 15.25, "uom" : "cm" }, "status" : "A" }Additional Query Tutorials
1、Query on Embedded/Nested Documents 查询嵌入/嵌套文档（字段值是一个文档）
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" }
])
> db.inventory.find( {} ,{_id:0})
{ "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" }Match an Embedded/Nested Document
查询size字段的值是{h:14,w:21,uom:"cm"}的所有文档：（在作为嵌入/嵌套文档的字段上指定相等条件）
{ "item" : "journal", "qty" : 25, "size" : { "h" : 14, "w" : 21, "uom" : "cm" }, "status" : "A" }db.inventory.find({size:{w:21,h:14,uom:"cm"}})
注：文档的精确匹配，包括顺序。
db.inventory.find（{size：{w：21，h：14，uom：“cm”}}）// 与集合中的任何文档不匹配
Query on Nested Field
Specify Equality Match on a Nested Field
查询size字段中嵌套的字段uom的值等于“in”的所有文档：
db.inventory.find( { "size.uom": "in" } )
{ "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" }Specify Match using Query Operator
查询size字段中嵌套的字段h的值小于15的所有文档：
db.inventory.find( { "size.h": { $lt: 15 } } )
{ "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" : "postcard", "qty" : 45, "size" : { "h" : 10, "w" : 15.25, "uom" : "cm" }, "status" : "A" }Specify AND Condition
查询size字段中嵌套的字段h的值小于15，uom的值为“in”，status的值为“D”的所有文档：
db.inventory.find( { "size.h": { $lt: 15 }, "size.uom": "in", status: "D" } )
{ "item" : "paper", "qty" : 100, "size" : { "h" : 8.5, "w" : 11, "uom" : "in" }, "status" : "D" }2、Query an Array 查询数组（字段值是一个数组）
db.inventory.insertMany([
{ item: "journal", qty: 25, tags: ["blank", "red"], dim_cm: [ 14, 21 ] },
{ item: "notebook", qty: 50, tags: ["red", "blank"], dim_cm: [ 14, 21 ] },
{ item: "paper", qty: 100, tags: ["red", "blank", "plain"], dim_cm: [ 14, 21 ] },
{ item: "planner", qty: 75, tags: ["blank", "red"], dim_cm: [ 22.85, 30 ] },
{ item: "postcard", qty: 45, tags: ["blue"], dim_cm: [ 10, 15.25 ] }
])
参考：
{ "item" : "journal", "qty" : 25, "tags" : [ "blank", "red" ], "dim_cm" : [ 14, 21 ] }
{ "item" : "notebook", "qty" : 50, "tags" : [ "red", "blank" ], "dim_cm" : [ 14, 21 ] }
{ "item" : "paper", "qty" : 100, "tags" : [ "red", "blank", "plain" ], "dim_cm" : [ 14, 21 ] }
{ "item" : "planner", "qty" : 75, "tags" : [ "blank", "red" ], "dim_cm" : [ 22.85, 30 ] }
{ "item" : "postcard", "qty" : 45, "tags" : [ "blue" ], "dim_cm" : [ 10, 15.25 ] }Match an Array
查询数组字段tags中正好包含两个元素“red和blank”，并且顺序相同的所有文档：
db.inventory.find( { tags: ["red", "blank"] } )
注：精确匹配，包括数组中元素的顺序。
{ "item" : "notebook", "qty" : 50, "tags" : [ "red", "blank" ], "dim_cm" : [ 14, 21 ] }查询数组字段tags中包含“red”和“blank”两个元素的所有文档，不考虑数组中的顺序和其他元素：
db.inventory.find( { tags: { $all: ["red", "blank"] } } )
等同于
db.inventory.find({$and: [ { tags: "red" }, { tags: "blank" }]},{_id:0})
{ "item" : "journal", "qty" : 25, "tags" : [ "blank", "red" ], "dim_cm" : [ 14, 21 ] }
{ "item" : "notebook", "qty" : 50, "tags" : [ "red", "blank" ], "dim_cm" : [ 14, 21 ] }
{ "item" : "paper", "qty" : 100, "tags" : [ "red", "blank", "plain" ], "dim_cm" : [ 14, 21 ] }
{ "item" : "planner", "qty" : 75, "tags" : [ "blank", "red" ], "dim_cm" : [ 22.85, 30 ] }Query an Array for an Element
查询数组字段tags中包含red元素的所有文档：
db.inventory.find( { tags: "red" } )
{ "item" : "journal", "qty" : 25, "tags" : [ "blank", "red" ], "dim_cm" : [ 14, 21 ] }
{ "item" : "notebook", "qty" : 50, "tags" : [ "red", "blank" ], "dim_cm" : [ 14, 21 ] }
{ "item" : "paper", "qty" : 100, "tags" : [ "red", "blank", "plain" ], "dim_cm" : [ 14, 21 ] }
{ "item" : "planner", "qty" : 75, "tags" : [ "blank", "red" ], "dim_cm" : [ 22.85, 30 ] }查询数组字段dim_cm中至少有一个元素的值大于25的所有文档：
db.inventory.find( { dim_cm: { $gt: 25 } } )
{ "item" : "planner", "qty" : 75, "tags" : [ "blank", "red" ], "dim_cm" : [ 22.85, 30 ] }Specify Multiple Conditions for Array Elements
Query an Array with Compound Filter Conditions on the Array Elements
查询数组字段dim_cn中一个元素的值大于15且另一个元素的值小于20，或者单个元素满足两个条件的所有文档：
db.inventory.find( { dim_cm: { $gt: 15, $lt: 20 } } )
{ "item" : "journal", "qty" : 25, "tags" : [ "blank", "red" ], "dim_cm" : [ 14, 21 ] }
{ "item" : "notebook", "qty" : 50, "tags" : [ "red", "blank" ], "dim_cm" : [ 14, 21 ] }
{ "item" : "paper", "qty" : 100, "tags" : [ "red", "blank", "plain" ], "dim_cm" : [ 14, 21 ] }
{ "item" : "postcard", "qty" : 45, "tags" : [ "blue" ], "dim_cm" : [ 10, 15.25 ] }Query for an Array Element that Meets Multiple Criteria 查询符合多个标准的数组元素
查询数组字段dim_cm中至少有一个元素的值大于22且小于30的所有文档：
db.inventory.find( { dim_cm: { $elemMatch: { $gt: 22, $lt: 30 } } } )
{ "item" : "planner", "qty" : 75, "tags" : [ "blank", "red" ], "dim_cm" : [ 22.85, 30 ] }Query for an Element by the Array Index Position 通过数组索引位置查询元素
查询数组字段dim_cm中第二个元素的值大于25的所有文档：
db.inventory.find( { "dim_cm.1": { $gt: 25 } } )
{ "item" : "planner", "qty" : 75, "tags" : [ "blank", "red" ], "dim_cm" : [ 22.85, 30 ] }Query an Array by Array Length
查询数组字段tags中具有三个元素的所有文档：
db.inventory.find( { "tags": { $size: 3 } } )
{ "item" : "paper", "qty" : 100, "tags" : [ "red", "blank", "plain" ], "dim_cm" : [ 14, 21 ] }3、Query an Array of Embedded Documents 查询嵌入式文档的数组（字段值包含数组，数组里面嵌套文档）
db.inventory.insertMany( [
{ item: "journal", instock: [ { warehouse: "A", qty: 5 }, { warehouse: "C", qty: 15 } ] },
{ item: "notebook", instock: [ { warehouse: "C", qty: 5 } ] },
{ item: "paper", instock: [ { warehouse: "A", qty: 60 }, { warehouse: "B", qty: 15 } ] },
{ item: "planner", instock: [ { warehouse: "A", qty: 40 }, { warehouse: "B", qty: 5 } ] },
{ item: "postcard", instock: [ { warehouse: "B", qty: 15 }, { warehouse: "C", qty: 35 } ] }
])
参考：
{ "item" : "journal", "instock" : [ { "warehouse" : "A", "qty" : 5 }, { "warehouse" : "C", "qty" : 15 } ] }
{ "item" : "notebook", "instock" : [ { "warehouse" : "C", "qty" : 5 } ] }
{ "item" : "paper", "instock" : [ { "warehouse" : "A", "qty" : 60 }, { "warehouse" : "B", "qty" : 15 } ] }
{ "item" : "planner", "instock" : [ { "warehouse" : "A", "qty" : 40 }, { "warehouse" : "B", "qty" : 5 } ] }
{ "item" : "postcard", "instock" : [ { "warehouse" : "B", "qty" : 15 }, { "warehouse" : "C", "qty" : 35 } ] }Query for a Document Nested in an Array 查询嵌套在数组中的文档
查询数组字段instock中的嵌入式文档与指定文档匹配的所有文档：
db.inventory.find( { "instock": { warehouse: "A", qty: 5 } } )
{ "item" : "journal", "instock" : [ { "warehouse" : "A", "qty" : 5 }, { "warehouse" : "C", "qty" : 15 } ] }注：精确匹配，包括字段的顺序。
db.inventory.find( { "instock": { qty: 5, warehouse: "A" } } ) //与集合中的任何文档不匹配。
