MongoDB authoritative Guide to learn notes 4---query related knowledge points

1 Find

Find ({query condition},{"key": 1, "email": 1}) after which keys are returned

2 Available comparison operators

$lt, $lte, $GT, $gte

such as Db.users.find ({"Age": {"$gte": +, "$lte": 30}})

3 Not equal to

Find (..... {"Key": {"$ne": "Value"}}

4 in

Find (..... {"Key": {"$in": [[i]}}

5 nin

Find (..... {"Key": {"$nin": [[i]}}

6 or

Find ({"$or": [{"Key1": "Value1"}, {"Key2": "Value2"}]})

Find ({"$or": [{"Key1": {"$in": ["value1", "Value2"]}}, {"Key2": "Value2"}]})

7$mod

Find ({"key": {"$mod": [5,1]}})

8 not

Find ({"key": {"$not": {"$mod": [5,1]}}})

9 and

Find ({"$and": [{"x": {"$lt": 1}}, {"X": 4}]})

This match {"x" [0,4]}

Equivalent to find ({"X": {"$lt": 1, "$in": [4]}})

10 about null

Find ({"Y": null})---will not only find the Y:null document, but also find a document that does not exist for this field.

can use

Find ({"Z": {"$in": [null], "$exists": True}})

11 queries using regular expressions ---PCRE

Query named Joe or Joe

Find ({"name":/joe/i})

Find ({"name":/joe?/i})

Find ({"name":/^joe/})

12 Querying arrays

Find ({"Fruit": "value1"}) that is the array contains value1 can be searched!

The 13 array contains multiple

Find ({"fruit": {"$all": ["value1", "Value2"]}}

That is, the array contains both value1 and value2

14 Exact Match

Find ({"Fruit": "value1", "value2"]})

The array contains and only contains these 2 values!

15 ordinal query of an array

Find ({"fruit.2": "Peach"})

16$size

Find ({"fruit": {"$size": 3}})

17$slice

FindOne (criteria,{"comments": {"$slice": 10}})

Return to top 10 reviews!

FindOne (criteria,{"comments": {"$slice":-10}})

Return to post 10 reviews!

FindOne (criteria,{"comments": {"$slice": "23,10"}})

Skip 23 elements and return as many as 10 elements!

Note that only the comments can be controlled, and the other fields still return!

$

mode:

Comments:[{name:bob,email:xxx}, ..........]

Find ({"Comments.name": "Bob"},{"comments.$": 1})

Returns the first matching document.

19 query for array

{"X": {"$GT": Ten, "$lt": 20}}

If x is an array at this point, then any one element satisfies 1 of the criteria to be considered a match!

But if it's not an array, match it at the same time!

20$elemmatch

First, only the array elements will be matched

Find ({"X": {"$elemMatch": {"$GT": Ten, "$lt": 20}})

21 If an index is created

Find ({"X": {"$GT": Ten, "$lt": $}}). min ({"X": Ten}). Max ({"X": 20})

The effect is very good! Because not all indexes are scanned, they are scanned in part of the index!

22 Querying inline documents

Find ({"name": {"First": "Joe", "Last": "Schmoe"}})---exact match!

The tragedy is that this kind of query is also sequential related!!!

Note: For inline documents, such queries are exact matches and must be done in the following way!

23 Better practices

Find ({"Name.first": "Joe", "Name.last": "Schmoe"})

Is it the relationship of or???

24 Please refer to $elemmatch Method!

25 The ultimate must kill skill-where

----------------about Cursors

Take 100 or 4MB at a time, whichever is smaller.

Find (). Skip (3). Limit ({"Key1": 1, "Key2": -1}). _addspecial ("$maxscan", 20)

. _addspecial ("$min", 20)

. _addspecial ("$max", 20)

. _addspecial ("$showDiskLoc": TRUE)

. SnapShot ()---will make the query slow!

Note: You can specify--noscripting when starting Mongod, turn off JS Run! ---Close the server-side script!