Shulou(Shulou.com)06/01 Report--

Vps2 "> https://docs.mongodb.com/manual/reference/method/db.collection.find/

Query document

Db.collection.find (query, projection)

Methods:

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"}

])

Reference:

> 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"}

The operation must be in the form of key-value pairs and must be enclosed in {}, so all queries must be enclosed in {} first.

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

The value of the query size field is all documents for {hburex 14 ~ (nd) ~ (21) Magi Uom: "cm"}: (specify equality conditions on fields that are embedded / nested documents)

{"item": "journal", "qty": 25, "size": {"h": 14, "w": 21, "uom": "cm"}, "status": "A"}

Db.inventory.find ({size: {wcm 21 ~ (st) HVR 14 ~ (th) Uom: "cm"}})

Note: exact matching of documents, including order.

Db.inventory.find ({size: {wcm 21 ~ (st) HVR 14 ~ (th) uom: "cm"}) / / does not match any documents in the collection

Query on Nested Field

Specify Equality Match on a Nested Field

Query all documents where the value of the field uom nested in the size field is equal to "in":

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

Query all documents whose value of the nested field h in the size field is less than 15:

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

Query all documents where the value of the nested field h in the size field is less than 15 and the value of in is "in" and the value of status is "D":

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 query array (field value is an array)

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]}

])

Reference:

{"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

Query all documents that have exactly two elements "red and blank" in the same order in the array field tags:

Db.inventory.find ({tags: ["red", "blank"]})

Note: exact matches, including the order of elements in the array.

{"item": "notebook", "qty": 50, "tags": ["red", "blank"], "dim_cm": [14,21]}

Query all documents in the array field tags that contain "red" and "blank" elements, regardless of the order and other elements in the array:

Db.inventory.find ({tags: {$all: ["red", "blank"]}})

Equivalent to

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

Query all documents that contain the red element in the array field tags:

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]}

Query all documents that have at least one element in the array field dim_cm whose value is greater than 25:

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

Query all documents in the array field dim_cn where the value of one element is greater than 15 and the value of another element is less than 20, or that a single element meets two conditions:

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 queries array elements that meet multiple criteria

Query all documents that have at least one element in the array field dim_cm whose value is greater than 22 and less than 30:

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 queries elements through array index location

Query all documents whose value of the second element in the array field dim_cm is greater than 25:

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

Query all documents with three elements in the array field tags:

Db.inventory.find ({"tags": {$size: 3}})

{"item": "paper", "qty": 100,100, "tags": ["red", "blank", "plain"], "dim_cm": [14,21]}

3. Query an Array of Embedded Documents queries the array of embedded documents (the field value contains the array, and the documents are nested in the array)

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}]}

])

Reference:

{"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 queries documents nested in an array

Query the embedded document in the array field instock for all documents that match the specified document:

Db.inventory.find ({"instock": {warehouse: "A", qty: 5}})

{"item": "journal", "instock": [{"warehouse": "A", "qty": 5}, {"warehouse": "C", "qty": 15}]}

Note: exact match, including the order of fields.

Db.inventory.find ({"instock": {qty: 5, warehouse: "A"}}) / / does not match any documents in the collection.

Specify a Query Condition on a Field in an Array of Documents

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