[mongodb] basic use of mongodb database, special cases, and the installation and creation process of mongoose (including the installation of mongoose fixed version)

MongoDB The comparison operator for

• KaTeX parse error: Expected '}', got 'EOF' at end of input: …tion.find({ Elements :{ lt: The number }})
• KaTeX parse error: Expected '}', got 'EOF' at end of input: …tion.find({ Elements :{ gt : The number }})
• KaTeX parse error: Expected '}', got 'EOF' at end of input: …tion.find({ Elements :{ gte: The number }})
• KaTeX parse error: Expected '}', got 'EOF' at end of input: …tion.find({ Elements :{ lte: The number }})
• KaTeX parse error: Expected '}', got 'EOF' at end of input: …tion.find({ Elements :{ ne: The number }})
• Interval judgment ( Multiple conditions can be passed in )
  • db.collection.find({ Elements :{ $gt:The\; number1,$lt: The number 2}})
  • Indicates greater than the value 1 And smaller than the array 2
• Multi condition interval judgment
  • db.collection.find({$or:[{ Elements : data 1},{ Elements : data 2},…]})
  • Indicates that the judgment element meets the data 1 Or meet the data 2 The situation of

MongoDB View fixed data

• When use ,- Never carry out without conditions - Query for

• Before viewing the collection 10 Data

  • db.collection.find().limit(10);

• see 11-20 Data

  • skip() Data used to skip a fixed number of entries
  • db.collection.find().skip(10).limit(10);

• Paging fixed formula

  • skip(( Page number -1)* Fixed number of entries per page ).limit( Fixed number of entries per page );

• Be careful ：

  • MongoDB Will automatically adjust skip and limit The order of

MongoDB Find special situations

• In direct use find() Method returns an array , Unable to get the value you need to find , You can use [0] or findOne() Method to find
• When the codes with the same meaning in two sets are inconsistent ( It is difficult to find when there are many data attributes , So try to make the code consistent when creating the set ), Create a variable to receive the value , Use this variable when searching in another set
• When querying, if the data does not appear correctly , Check the data type of query criteria , The result may be abnormal due to inconsistent data types
• When you only want to find individual data when querying , You can set the projection of query results at the position of the second parameter ( When using projection 1 Presentation display ,0 Means not to show ,_id Default display )
  • db.collection.find({},{ Elements 1:1, Elements 2:0,…})

MongoDB Modify the value ( Increase or decrease )

• $inc increase ( Reduce ) The number (increment)
• db.collection.updateMany({ Conditions },{$inc:{ Modify the content }})

MongoDB Sort the data

• MongoDB The default is to use _id Sort
• have access to sort() Method needs to pass an object to specify the collation of the document (1 Arrange... In ascending order ,-1 Represents a descending order ), You can also pass multiple objects
  • db.collection.find().sort( Elements 1:1, Elements 2:-1,…);
  • Use elements first 1 Sort in ascending order , When element 1 Phase at the same time , On the element 2 Sort in descending order

Mongoose

• Use steps ：
  • Enter command in terminal npm i [email protected]( Version number )
  • Linked database
  • Create constraints Schema
  • Create a module Model

Be careful

• limit() skip() sort() It can be written in any order