Document Database MongoDB Summary

MongoDB has many advantages, such as multi-column indexes. Some statistical functions can be used for queries and multi-condition queries are supported. However, multi-table queries are not currently supported, you can try to solve the problem of multi-Table query through data redundancy.
   MongoDB provides a wealth of data operations. The following are some examples. Most of the content is from the official documentation, and others are for your understanding.
   Query all colls data
   DB. colls. Find () // select * From colls
   Query by specified conditions
   DB. colls. Find ({'last _ name': 'Smith '}); // select * From colls where last_name = 'Smith'
   Specify multi-condition Query
   DB. colls. Find ({X: 3, Y: "foo"}); // select * From colls where x = 3 and Y = 'foo'
   Query by specified condition range
   DB. colls. Find ({J: {$ ne: 3}, K: {$ GT: 10}); // select * From colls where J! = 3 and K> 10
   The query does not include any content.
   DB. colls. Find ({}, {A: 0}); // query all data except that A is 0.
   Supported <, <=,>,> =, and must be replaced by $ lt, $ LTE, $ GT, and $ GTE.
   DB. colls. Find ({"field": {$ GT: Value }}); 
   DB. colls. Find ({"field": {$ LT: Value }}); 
   DB. colls. Find ({"field": {$ GTE: Value }});
   DB. colls. Find ({"field": {$ LTE: Value }});
   You can also query the range of a field.
   DB. colls. Find ({"field": {$ GT: value1, $ LT: value2 }});
   Not equal to $ ne
   DB. colls. Find ({x :{$ ne: 3 }});
   Character $ in for in Query
   DB. colls. Find ({"field": {$ in: array }});
   DB. colls. Find ({J: {$ in: [2, 4, 6]});
   Not in query character $ Nin
   DB. colls. Find ({J: {$ Nin: [2, 4, 6]});
   MoD query character $ mod
   DB. colls. Find ({A: {$ mod: [10, 1]}) // Where a % 10 = 1
   $ All Query
   DB. colls. Find ({A :{$ All: [2, 3] }}); // when specifying a to satisfy any value in the array
   $ Size Query
   DB. colls. Find ({A: {$ size: 1}); // queries the number of objects. This query queries records with the number of sub-objects of a being 1.
   $ Exists Query
   DB. colls. Find ({A: {$ exists: true}); // data of object
   DB. colls. Find ({A :{$ exists: false }}); // The data of object A does not exist.
   $ Type query $ the type value is the unique value of bsonhttp: // bsonspec.org/data
   DB. colls. Find ({A: {$ type: 2}); // match data of the string type as
   DB. colls. Find ({A: {$ type: 16}); // match a as int type data
   Match with regular expressions
   DB. colls. Find ({Name:/acme. * Corp/I}); // similar to like
   Embedded object query
   DB. colls. Find ({"author. Name": "Joe "});
   Version 1.3.3 and later include $ not query
   DB. colls. Find ({Name: {$ not:/acme. * Corp/I }});
   DB. colls. Find ({A :{$ not :{$ mod: [10, 1] }}});
   Sort () sorting
   DB. colls. Find (). Sort ({ts:-1}); // 1 is in ascending order. 2 is in descending order.
   Limit () Limit the number of returned data queries
   DB. colls. Find (). Limit (10)
   Skip () skips some data
   DB. colls. Find (). Skip (10)
   Snapshot () snapshot ensures that no duplicate data is returned or objects are lost
   Count () count the number of queried objects
   DB. Students. Find ({'address. state': 'CA'}). Count (); // High Efficiency
   DB. Students. Find ({'address. state': 'CA'}). toarray (). length; // very inefficient
   The group () function for query result grouping is similar to the group by function in SQL.
   Distinct () returns a non-repeated Value

 From the above, we can see that there are many ways to query MongoDB, which can be used in combination. The common sum statistics function is not currently supported by MongoDB.

 

Java code

Querybuilder = new querybuilder (); querybuilder. And (key). Is (value );

You can also use querybuilder. Start (key). Is (value). Get () to obtain a dbobject object for query.
The above key is the key to be queried, and the value is the matched value.
Then use

Java code

Collection. Find (querybuilder. Get ())

Query
The query result is dbcusor.
You can use querybuilder. And (key). Is (value). And (key). Is (value) to query multiple key values.

And, the available query methods include lessthan, equals, exists, greaterthan, greaterthanequals, In, lessthan, lessthanequals, Mod, notequals, notin, and RegEx.