Sort basic MongoDB queries

Exact match

• For a single key-Value Pair: {"age": 28}, all documents whose "age" value is 28 are returned.
• Multiple key-value pairs: {"username": "tom", "age": 28} combine multiple query conditions, equivalent: condition 1 AND condition 2 AND... AND condition N. This query document returns all documents whose username is tom and their age is 28.

Condition match Range

• "$ Lt", "$ lte", "$ gt", "$ gte"
  Comparison operators:
  

  <    $lt <=   $lte>    $gt>=   $gte

  
  You can combine them to find values in a range.
  For example, the query documents between 18 and 35 are: {"age": {"$ gte": 18, "$ lte": 35 }}
  This range query method is especially convenient for date type values.

• "$ Ne"
  "Not equal" operator, corresponding :! =
  If the user name is not tom, the query document is: {"username": {"$ ne": "tom "}}

OR Query

• $ In
  Queries multiple values corresponding to a key and performs OR queries on a single key.
  For example, if the number of winning events is or 8, you need to find out the query documents for all the winning data: {"ticket_no": {"$ in": [1, 4, 8]}
• $ Nin
  Correspondingly, $ nin returns data that does not match the values in the array. For example, the query document for finding data that does not win the prize is: {"ticket_no": {"$ nin": [1, 4, 8]}.
• $ Or
  It is more common to query any value of multiple keys. It accepts an array of all possible conditions as a parameter, or it can contain other conditions. For example:
  

  {     "$or": [        {            "ticket_no":{                "$in":[1, 4, 8]            }        },         {            "winner":true        }    ]}

  
  The first condition of $ or should be matched to more documents as much as possible, so as to be the most effective.

$ Not

$ Not is a metaconditional sentence. It can be used on any other condition and the table is reversed.
For example: Query document: {"value": {"$ mod": [5, 1]}. The values that meet the criteria include: 1, 6, and 11.
To search for data with values of 2, 3, 4, 5, 7, 8, 9, 10, and 12, you can use: {"value": {"$ not ": {"$ mod": [5, 1]}.

$ Exists

Used to query whether a key exists in the document. For example, find the document with the key name key1: {"key1": {"$ exists": false} that does not exist }};
Conversely, {"key1": {"$ exists": true} indicates that the key1 key exists.

Type match Null

Query the document {"x": null}. After the statement is executed, it returns the document containing the key-Value Pair "x": null, and the document without the x key.

Regular Expression

All the regular expressions supported by PCRE can be accepted by MongoDB.
If the query document {key1 "} is returned.
It can be used in like scenarios in SQL.

Query Arrays Each element in the array is the value of the entire key. If any:

Document 1: {"fruit": ["apple", "pear", "peach"]}, document 2: {"fruit": ["peach", "banana ", "apple"]}, document 3: {"fruit": ["orange", "banana", "apple"]},

• Single element matching
  If the query document is {"fruit": "apple"}, documents 1, 2, and 3 are matched successfully.

• Match Multiple Elements
  The $ all clause is required. If the query document is {"fruit": {"$ all": ["apple", "peach"]}, the document 1 and 2 will be matched and irrelevant to the element sequence.

• Exact match
  If the query document is: {"fruit": ["apple", "pear", "peach"]}, only document 1 is matched. for missing or redundant documents, and those with different orders won't match.

• Subscript matching
  The key. index method is used, and the array subscript starts from 0. For example, if you query the document {"fruit.2": "apple"}, the document 2 and 3 will be matched.

• Length matching
  If the query document is: {"fruit": {"$ size": 3 }}, it indicates an array with a length of 3. the query documents 1, 2, and 3 will be matched.

Query of embedded documents

• Point representation
  For example:
  

  {    "_id":1,    "name":{"first":"Joe", "last":"Smith"}}

  
  You can query: {"name. first": "Joe", "name. last": "Smith "}

• $ ElemMatch
  It is used when multiple key operations are required for an embedded document.
  If any:
  

  {  "comments": [    {      "name": "Tom",      "score": 3,      "comment": "bad"     },    {      "name": "Jim",      "score": 6,      "comment": "good"     }  ]}

  
  To search for comments whose Tom scores are greater than 5, you can only: {"comments": {"$ elemMatch": {"name": "Tom", "score ": {"$ gt": 5 }}}}
  But it cannot: {"comments": {"name": "Tom", "score": {"$ gt": 5 }}. it cannot match the "comment" key.
  Or {"comments. name": "Tom", "comments. score": {"$ gt": 5}, not the same comment.