MongoDB

Introductory Remarks: db.keyword.distinct ("keyword"). length As follows: Db.keyword.distinct ("keyword"). length View the total number of records in the keyword field in the keyword table without duplicates This method is not seen in the

Use command MongoDB use database_name Used to create the database. The command creates a new database and returns the existing database if it does not exist. Dropdatabase () method MongoDB Db.dropdatabase () The command is used to delete an

Indexing is the most effective means of improving query query efficiency. An index is a special data structure that stores portions of the data in an easy-to-traverse format (for example, a specific field or set of field values), which sorts the

Exception in thread "main" java.lang.IllegalAccessError:tried to access method Org.bson.types.ObjectId. (III) V from class Org.mongojack.internal.stream.ObjectIdConvertor. The cause of this problem is caused by a jar version

Overview The _id field of MongoDB exists as a primary key at the top level of all documents, and _id must be unique and always have a unique constraint index. In addition to the unique constraint, you can use any value on the _id field in the

Use $set to specify a value for a key, and if it does not exist, create it. This is useful for updating patterns or adding user definitions. Db.user.insert ({"Name": "Codingwhy.com"}) This user now only has the name information and now needs to

resolves a MongoDB cursor ID is not a valid at server issue When you use Db.collection.find (), it returns not all data, but actually a "cursor". Its default behavior is to query the database for the first 101 documents, or 1 MB of documents,

Today, when configuring MongoDB, Win10 encountered a small problem, the configuration for the service is always not configured, the results found that the following command is not running as an administrator, resulting in failure.

Title Resolve MongoDB E11000 Duplicate key error collection: **.customer index:id dup key,Or the MongoDB atomicity problem, the code is as follows: Collection.updateone ( New Document () Append ("_id", _id). Append ("$isolated", 1), New

Gridfs is a file specification for storing large files in MongoDB:The MongoDB database holds binary objects in support of the Bson format , but the Bson objects in MongoDB cannot exceed 4MB in maximum.The GRIDFS specification provides a transparent

@Override public Ordercfeecode Selectbyprimarykey (String feecode) {criteria = new Crite Ria (); Criteria.oroperator (Criteria.where ("Feecode"). is (Feecode), Criter Ia.where ("Reffeeact"). is (Feecode),

MongoDB Basic Command Summary MONGO additions and deletions change Batch update based on query criteria > DB. Goodsinfo.update ({"Type": 1}, {$set: {"name": "Birdben"}}, False, True); Delete data for a specified condition > DB. Goodsinfo.remove (

First, download and install MongoDB 1, official website download: https://www.mongodb.com/download-center#community 2. Installation 3, configure the path, as shown in the following image: Execute mongod.exe command, error "C:\data\db\ not

The MongoDB remove () function is used to remove data from the collection. The update () function can be used for MONGODB data updates. It is a good practice to execute the Find () command before executing the Remove () function to determine if the

The example is based on the current latest MONGO driver, version Mongo-2.10.1.jar, and unit tests written in JUnit. Testcase.java Java code    package com.wujintao.mongo;      import  java.net.unknownhostexception;   import java.util.arraylist;  

Basic Operation command Show DBS//View all libraries using test//Use library without words automatically create show collections//view created table add Db.test_collection.insert (); Key value pair JSON data for (i=3;iDb.test.find ({$text: {$search:

MONGO Warning: 2016-09-05t10:55:13.241+0800 I CONTROL [initandlisten] * * WARNING:/sys/kernel/mm/transparent_hugepage/enabled is ' Always '.2016-09-05t10:55:13.241+0800 I CONTROL [initandlisten] * * We suggest setting it to ' never '2016-09-05t10:55

MongoDB Limit () method If you need to read a specified number of data records in MongoDB, you can use the MongoDB limit method, and the limit () method accepts a numeric parameter that specifies the number of record bars read from MongoDB. Grammar

Transferred from: http://docs.mongoing.com/manual-zh/core/aggregation-pipeline-optimization.html $skip + $limit order optimization If you have a pipeline with $skip followed by a $limit, the optimizer moves the $limit to the front of the $skip, at

MongoDB implements MySQL auto_increment function Refer to the official documentation (FINDANDMODIFY implementation): 1.Insert into the counters collection, the initial value for the UserID: Db.counters.insert ( { _id: "userid", seq:0