MongoDB queries the documentation

MongoDB queries the documentation

Grammar

The syntax format for MongoDB query data is as follows:

>db.COLLECTION_NAME.find()

The find() method displays all documents in an unstructured manner.

If you need to read the data in an easy-to-read way, you can use the pretty() method in the following syntax format:

>db.col.find().pretty()

The pretty() method displays all documents in a formatted manner.

Instance

The following example we query the data in the collection col:

> db.col.find().pretty()
{
        "_id" : ObjectId("56063f17ade2f21f36b03133"),
        "title" : "MongoDB 教程",
        "description" : "MongoDB 是一个 Nosql 数据库",
        "by" : "w3cschool",
        "url" : "http://www.w3cschool.cn",
        "tags" : [
                "mongodb",
                "database",
                "NoSQL"
        ],
        "likes" : 100
}

In addition to the find() method, there is a findOne() method that returns only one document.

MongoDB is compared to the RDBMS Where statement

If you are familiar with regular SQL data, the following table gives you a better understanding of MongoDB's conditional statement queries:

MongoDB AND condition

MongoDB's find() method can pass in multiple keys (keys), each separated by a comma, and the AND condition of regular SQL.

The syntax format is as follows:

>db.col.find({key1:value1, key2:value2}).pretty()

Instance

The following example queries the data for the MongoDB tutorial in w3cschool with the by and title keys

> db.col.find({"by":"w3cschool", "title":"MongoDB 教程"}).pretty()
{
        "_id" : ObjectId("56063f17ade2f21f36b03133"),
        "title" : "MongoDB 教程",
        "description" : "MongoDB 是一个 Nosql 数据库",
        "by" : "w3cschool",
        "url" : "http://www.w3cschool.cn",
        "tags" : [
                "mongodb",
                "database",
                "NoSQL"
        ],
        "likes" : 100
}

The above example is similar to the WHERE statement: WHERE by 'w3cschool' AND title 'MongoDB Tutorial'

MongoDB OR condition

The MongoDB OR conditional statement uses the keyword $or, in the following syntax format:

>db.col.find(
   {
      $or: [
	     {key1: value1}, {key2:value2}
      ]
   }
).pretty()

Instance

In the following example, we demonstrated a document with a query key by value of w3cschool or a key title value of MongoDB tutorial.

>db.col.find({$or:[{"by":"w3cschool"},{"title": "MongoDB 教程"}]}).pretty()
{
        "_id" : ObjectId("56063f17ade2f21f36b03133"),
        "title" : "MongoDB 教程",
        "description" : "MongoDB 是一个 Nosql 数据库",
        "by" : "w3cschool",
        "url" : "http://www.w3cschool.cn",
        "tags" : [
                "mongodb",
                "database",
                "NoSQL"
        ],
        "likes" : 100
}
>

AND and OR are used in union

The following example demonstrates the joint use of AND and OR, similar to the general SQL statement: 'Where likes sgt;50 AND (by s'w3cschool' OR title s'MongoDB tutorial').

>db.col.find({"likes": {$gt:50}, $or: [{"by": "w3cschool"},{"title": "MongoDB 教程"}]}).pretty()
{
        "_id" : ObjectId("56063f17ade2f21f36b03133"),
        "title" : "MongoDB 教程",
        "description" : "MongoDB 是一个 Nosql 数据库",
        "by" : "w3cschool",
        "url" : "http://www.w3cschool.cn",
        "tags" : [
                "mongodb",
                "database",
                "NoSQL"
        ],
        "likes" : 100
}