The general method of using Java to operate MongoDB query

Java operates mongodb to query, and the common filter conditions are set as follows:

List of conditions:
BasicDBList cOndList= new BasicDBList();
Temporary condition object:
BasicDBObject cOnd= null;
DBCollection coll = db. getCollection(“A”);

1. $where
In a certain application, if you want to set A to query documents and satisfy certain attribute operation results in the documents, you can write a script function and use where to set it, for example:
User information stored in a collection, including name, age, mobile phone number, address, etc., to filter out users whose age is greater than 20 and less than or equal to 40, we can do this:
String ageStr = “function (){return parseFloat(this.age) > 20
&& parseFloat(this.age) <= 40};";
cOnd= new BasicDBObject();
cond. put(“$where”, ageStr);

Put in conditional list
condList. add(cond);

2. $in
In example 1, to query user information with ages 23, 40, and 50, we can do this:
Create a temporary condition list object and add condition values ​​to it
BasicDBList values ​​= new BasicDBList();
values.add(23);
values.add(40);
values. add(50);

cOnd= new BasicDBObject();
cond.put(“age”,new BasicDBObject(“$in”,values));

Put in conditional list
condList. add(cond);

3. Fuzzy matching
In example 1, to perform fuzzy query according to the user’s name, such as: Wang, we can do this:

Use case-insensitive fuzzy queries
3.1 Exact match
Pattern pattern = Pattern.compile(“^王$”,
Pattern.CASE_INSENSITIVE);
3.2 Right match
Pattern pattern = Pattern.compile(“^.*王$”,
Pattern.CASE_INSENSITIVE);
3.3 Left match
Pattern pattern = Pattern.compile(“^王.*$”,
Pattern.CASE_INSENSITIVE);
3.4 Fuzzy matching
Pattern pattern = Pattern.compile(“^.*王.*$”,
Pattern.CASE_INSENSITIVE);

cOnd= new BasicDBObject();
cond. put(“name”,cond);

Put in conditional list
condList. add(cond);

4. $gte/$lte/$gt/$lt
In example 1, to filter out users whose age is greater than 20 and less than or equal to 40, we can do this:
cOnd= new BasicDBObject();
cond.append(“age”,new BasicDBObject(“$gt”,20));
cond.append(“age”,new BasicDBObject(“$lte”,40));

Put in conditional list
condList. add(cond);

There may be multiple conditions for filtering in daily queries, and the relationship between multiple conditions is and, combined with the above examples 1, 2, 3, and 4
Adding each condition to the list of conditions, I can do this:
BasicDBObject searchCOnd= new BasicDBObject();
searchCond. put(“$and”, condList);

Then query the data:
DBCursor ret = coll. find(searchCond);

The above is the setting method of commonly used filter conditions, and others will be updated later.