MongoDB Query operation

Query by criteria

Compare operations:$lt, $lte, $gt, $gte, $ne

Db.user.find ({"score": {$gt:}});

$or : Contains multiple conditions, the relationship between them for or, $nor equivalent to or take the inverse

Db.user.find ({$or: [{"score": {$gt:}},{"user_id") :"U3"}]});

$not: used as the other condition, take the inverse

$mod: Divides the value of the query by the first given value, if the remainder equals equal to two values, the match succeeds

Db.user.find ({"score": {$mod: [4,1]}});

$in : Query Multiple values for a key, as long as the key matches one of them, $nin to not contain

Db.user.find ({"score": {$ in: [+]}});

$all : The key needs to match all the values

Db.user.find ({"House": {$all: [All]}});

$exists: checks if a key exists, 1 is present, and 0 indicates that it does not exist

Db.user.find ({"name": {$exists: 1}});

NULL Type: not only can match the value of the key is null, but also match the condition that the key does not exist

Db.user.find ({"name":null});

Querying arrays

a single element matches , just like the previous write condition, {key:value}

Db.user.find ({"House":);

multiple elements match , using $all, {key:{$all: [A, B]}}, the order of the elements does not matter

Db.user.find ({"House": {$all: [+]}});

You can use an index to specify a specific location for the query array, {"Key. Index number": Value}

Db.user.find ({"house.1":+);

Query an array of length, using the $size

Db.user.find ({"House": {$size:2}});

Specify a subset, use a $slice, positive numbers are the number of front bars, negative numbers are the number of tails, you can specify the offset and how many elements to return, such as: $slice: [50,10]

Db.user.find ({"House": {$exists:1}},{" House ": {$slice: [0,2]}});

You can use $ to specify any of the array elements that match the criteria, such as: {"users.$": 1}

Db.user.find ({"House": {$exists:1}},{"house.$": 1});

$elemMatch: Requires multiple conditional statements to be used to compare an array element

Db.user.find ({"House": {$elemMatch: {$gte:$, $lt:+}});

command to query the number of record bars: Count

Db.user.find (). Count ();

If you want to get the number of bars logged after a conditional query, you need to specify count (True or not 0)

• command to limit the number of record entries returned: limit (number of bars to return)
• command to limit the starting point of the number of records returned: Skip (return from the first few)
• Sorted Commands: Sort ({fields to sort: 1 for ascending,-1 for descending})

Db.user.find ({}). Limit (2). Count (1);

Db.user.find ({}). Skip (1). Limit (2);

Db.user.find ({}). Sort ({"Score": 1});

Paged query: Combining Limit,skipt and sort
Of course, you can also use other means of paging, such as using a custom ID, and then pagination according to the ID

Querying all non-duplicated data for a given key, command: DISTINCT
Syntax: Db.runcommand ({"DISTINCT": Collection name, "Key": "field with no duplicate data"});

Db.runcommand ({"distinct":"user","key ":"user_id"});

Stored Procedures
MongoDB's stored procedure is actually a custom JS function.
Use Db.system.js.save ({"_id": Name, Value: function});

var return A +b;}; Db.system.js.save ({"_id":"myF","value  ": Totalf});

Can be viewed by the following command: Db.system.js.find ();
Can be called by the following command: Db.eval (name)

Db.eval ("MyF (1,3)");

MongoDB Query operation