. 1, $ type operator
1.1, $ type to retrieve the set of data types based on matching the type of BSON, and returns the result;
The BSON : one kind of computer data interchange format , is used mainly as a MongoDB database in data storage and network transmission format;
It is a binary representation , the data can be used to represent a simple structure, associative array (MongoDB referred to as "object" or "document") and MongoDB various data types;
BSON name due to JSON, meaning Binary JSON (binary JSON);
eg:db.col.find({"title" : {$type : 'string'}});
2, conditions operation marks
2.1, (>) is greater than - $ gt
2.2 (<) is less than - $ lt
2.3 (> =) or greater - $ gte
2.4 (<=) or less - $ lte
eg:db.col.find({likes : {$gt : 100}}) 、db.col.find({likes : {$lt :200, $gt : 100}})