MongoDB Query Document

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, which has the following syntax:

>db.  Col.  Find().  Pretty()       

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

Instance

The following examples let us query the data in the set col:

>Db.Ao..Find().Pretty(){ "_ID" : ObjectId("56063f17ade2f21f36b03133"), "Title" : "MongoDB Tutorial", "description" : "MongoDB is a Nosql database", "By" :  "rookie Tutorial" ,  "url"  :  "http://www.runoob.com" ,  "tags"  :[  "MongoDB" ,  "database" ,  "NoSQL"  ],  "likes"  :  100}        

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

MongoDB versus RDBMS Where statement comparison

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

Operation	format	Example	similar statements in an RDBMS
Equals	{<key>:<value>}	db.col.find({"by":"菜鸟教程"}).pretty()	where by = ‘菜鸟教程‘
Less than	{<key>:{$lt:<value>}}	db.col.find({"likes":{$lt:50}}).pretty()	where likes < 50
Less than or equal to	{<key>:{$lte:<value>}}	db.col.find({"likes":{$lte:50}}).pretty()	where likes <= 50
Greater than	{<key>:{$gt:<value>}}	db.col.find({"likes":{$gt:50}}).pretty()	where likes > 50
Greater than or equal to	{<key>:{$gte:<value>}}	db.col.find({"likes":{$gte:50}}).pretty()	where likes >= 50
Not equal to	{<key>:{$ne:<value>}}	db.col.find({"likes":{$ne:50}}).pretty()	where likes != 50

MongoDB and condition

The MongoDB find () method can pass in multiple keys (key), each separated by commas, and the regular SQL and condition.

The syntax format is as follows:

>db.  Col.  Find({key1:value1, key2:value2}).  Pretty()               

Instance

The following example uses the by and title keys to query the data for the MongoDB tutorial in the rookie tutorial

>Db.Col.Find({"By":"Beginner's Tutorial", "Title":"MongoDB Tutorial"}).Pretty(){ "_ID" : ObjectId("56063f17ade2f21f36b03133"), "Title" : "MongoDB Tutorial", "description" : "MongoDB is a Nosql database", "By" :  "rookie Tutorial" ,  "url"  :  "http://www.runoob.com" ,  "tags"  :[  "MongoDB" ,  "database" ,  "NoSQL"  ],  "likes"  :  100}        

The above example is similar to the WHERE statement:where by= ' rookie tutorial ' and title= ' MongoDB tutorial '

MongoDB OR Condition

The MongoDB OR conditional statement uses the keyword $orin the following syntax format:

>db.  Col.  Find({ $or:[{key1: value1},{key2:value2} ]}). Pretty()                 

Instance

In the following example, we demonstrate the query key by value for the Novice tutorial or the key title value for the MongoDB tutorial document.

>Db.Ao..Find({$or:[{"By":"Beginner's Tutorial"},{"Title": "MongoDB Tutorial"}]}).Pretty(){ "_ID" : ObjectId("56063f17ade2f21f36b03133"), "Title" : "MongoDB Tutorial", "description" : "MongoDB is a Nosql database", "By" : "Rookie Tutorial", "url" : "http://www.runoob.com", "tags" : [  "MongoDB", "database", "NoSQL" ], "likes" :  >               

Combined with and OR

The following examples demonstrate the combined use of and and or, similar to the general SQL statement: ' where likes>50 and (by = ' Rookie Tutorial ' OR title = ' MongoDB tutorial ') '

>Db.Col.Find({"Likes": {$gt:50},$or: [{"By": "Beginner's Tutorial"},{"Title": "MongoDB Tutorial"}]}).Pretty(){ "_ID" : ObjectId("56063f17ade2f21f36b03133"), "Title" : "MongoDB Tutorial", "description" : "MongoDB is a Nosql database", "By" :  "rookie Tutorial" ,  "url"  :  "http://www.runoob.com" ,  "tags"  :[  "MongoDB" ,  "database" ,  "NoSQL"  ],  "likes"  :  100}        

MongoDB Query Document