MongoDb Read

1	db.coll.findOne() // returns a single document
2	db.coll.find()    // returns a cursor - show 20 results - "it" to display more
3	db.coll.find().pretty()
4	db.coll.find({name: "Max", age: 32}) // implicit logical "AND".
5	db.coll.find({date: ISODate("2020-09-25T13:57:17.180Z")})
6	db.coll.find({name: "Max", age: 32}).explain("executionStats") // or "queryPlanner" or "allPlansExecution"
7	db.coll.distinct("name")
8	
9	// Count
10	db.coll.count({age: 32})          // estimation based on collection metadata
11	db.coll.estimatedDocumentCount()  // estimation based on collection metadata
12	db.coll.countDocuments({age: 32}) // alias for an aggregation pipeline - accurate count
13	
14	// Comparison
15	db.coll.find({"year": {$gt: 1970}})
16	db.coll.find({"year": {$gte: 1970}})
17	db.coll.find({"year": {$lt: 1970}})
18	db.coll.find({"year": {$lte: 1970}})
19	db.coll.find({"year": {$ne: 1970}})
20	db.coll.find({"year": {$in: [1958, 1959]}})
21	db.coll.find({"year": {$nin: [1958, 1959]}})
22	
23	// Logical
24	db.coll.find({name:{$not: {$eq: "Max"}}})
25	db.coll.find({$or: [{"year" : 1958}, {"year" : 1959}]})
26	db.coll.find({$nor: [{price: 1.99}, {sale: true}]})
27	db.coll.find({
28	  $and: [
29	    {$or: [{qty: {$lt :10}}, {qty :{$gt: 50}}]},
30	    {$or: [{sale: true}, {price: {$lt: 5 }}]}
31	  ]
32	})
33	
34	// Element
35	db.coll.find({name: {$exists: true}})
36	db.coll.find({"zipCode": {$type: 2 }})
37	db.coll.find({"zipCode": {$type: "string"}})
38	
39	// Aggregation Pipeline
40	db.coll.aggregate([
41	  {$match: {status: "A"}},
42	  {$group: {_id: "$cust_id", total: {$sum: "$amount"}}},
43	  {$sort: {total: -1}}
44	])
45	
46	// Text search with a "text" index
47	db.coll.find({$text: {$search: "cake"}}, {score: {$meta: "textScore"}}).sort({score: {$meta: "textScore"}})
48	
49	// Regex
50	db.coll.find({name: /^Max/})   // regex: starts by letter "M"
51	db.coll.find({name: /^Max$/i}) // regex case insensitive
52	
53	// Array
54	db.coll.find({tags: {$all: ["Realm", "Charts"]}})
55	db.coll.find({field: {$size: 2}}) // impossible to index - prefer storing the size of the array & update it
56	db.coll.find({results: {$elemMatch: {product: "xyz", score: {$gte: 8}}}})
57	
58	// Projections
59	db.coll.find({"x": 1}, {"actors": 1})               // actors + _id
60	db.coll.find({"x": 1}, {"actors": 1, "_id": 0})     // actors
61	db.coll.find({"x": 1}, {"actors": 0, "summary": 0}) // all but "actors" and "summary"
62	
63	// Sort, skip, limit
64	db.coll.find({}).sort({"year": 1, "rating": -1}).skip(10).limit(3)
65	
66	// Read Concern
67	db.coll.find().readConcern("majority")

Source: mongodb.com

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