MongoDB find by id

Introduction to MongoDB find by id

The following article provides an outline for MongoDB find by id. MongoDB provides a function with the name findById() which is used to retrieve the document matching the ‘id’ as specified by the user. In order to use findById in MongoDB, find() function is used. If no document is found matching the specified ‘id’, it returns null. It is one of the important functions which is used widely when there is a need to retrieve the document according to their ids. Though many languages can use the MongoDB database, in order to perform their database task, it also depends on the language specifications as they vary from each other when it comes to usage of the function.

Syntax of MongoDB find by id

Given below is the basic syntax of using the find by id in a MongoDB database:

find() function is used in order to use find by id in MongoDB.

db.collection_name.find(query, projection)

Where,

• query: It is an optional parameter. It specifies the selection filter using the operators of the query. This parameter can be omitted in order to return all the documents in a collection.
• projection: It is an optional parameter. It specifies the field which will return matching the query filter. This parameter can be omitted in order to return all the fields in the matching documents.

Return type:

It returns the cursor to the documents which match the query criteria.

How does find by id Work in MongoDB?

• As the name suggests, find by id is used to retrieve the details of the document matching the particular ‘id’ provided by the user where ‘id’ is the automatically generated ‘id’ when a document is created in the database.
• When the user calls findById(_id) in Mongoose, it automatically calls findOne({_id}) which means that the findById calls findOne in the middle.
• Casting of queries is done in Mongoose in order to match the schema. ‘Id’ passed by the user is in a string that is converted to ObjectId by Mongoose.
• The ‘_id’ passed is the automatically generated id when a document is inserted in the database.
• In order to retrieve the automatically generated id, a simple ‘find()’ function can be used without specifying any criteria.
• In Mongosh, db.collection_name.find() will automatically iterates the cursor and display upto the first 20 documents of the collection.
• Different languages use different ways in order to retrieve or find the documents by specifying the id.

Examples of MongoDB find by id

Given below are some of the examples showing the usage of find by id in a MongoDB database. Consider the following conditions:

• There is a database already present with the name ‘db’.
• There is a collection in the database with the name ‘myCol’.
• All the documents are inserted in the collection ‘myCol’ using the insert function.

Example #1

Using the find() function without any parameters.

Code:

db.myCol.find();

Output:

Explanation:

• In the above example, the find() function of MongoDB is used without passing any parameter. Since none of the parameters is passed, find() function will retrieve all the detailed documents present in the collection. We can see that an additional field of ObjectId is automatically inserted at the starting of each document.
• MongoDB inserts the ObjectId for every new document inserted by the user. This objectId is unique and cannot be the same for two or more documents. It is one of the easiest ways to retrieve the ObjectId of all the documents and use it further according to the specific requirements.

Example #2

Using the find() function and passing the ObjectId parameter in it.

Code:

db.myCol.find({_id : ObjectId("60f532903ded77001064ae92")});

Output:

Explanation:

• In the above example, the document is found on the basis of the ObjectId of the document. ObjectId is the unique id that is automatically allocated when a new document is inserted into the collection.
• We can provide the ObjectId as a parameter of the find() function in MongoDB and its respective document is displayed on the console to the user.

Example #3

Using the find() function by passing the parameters of the fields other than the unique objectId.

Code:

db.myCol.find({"name" : "sunita"});

Output:

Explanation:

• As we can see in the above example, the user can also put the parameter of find function of the other fields of the document.
• As the “name” is also a field on which each document can be filtered, so the document having the “name” as “sunita” is found and all its details are displayed to the user on the console.

Suppose there are two or more documents in the collections having the same value for the particular field.bLet see the situation with the help of the data present in the collection similar to the one given below:

Code:

db.myCol.find();

Output:

Example #4

Using the find() function and passing the parameter of the field which is the same for more than one record.

Code:

db.myCol.find({"city" :"agra"});

Output:

Explanation:

• In the above example, as we can see that there is more than one document present in the collection having the field “city” as “agra”. So when we pass the parameter of “city” : “agra”, all the documents matching the criteria will be displayed to the user on the console. It is never the case of find() function that only one record will be retrieved at a time.
• In the case of ObjectId only one document would be displayed to the user as it is unique to each document and can never be the same. Else for the other cases, all the documents satisfying the condition mentioned in the find() parameters would be displayed to the user on the console.

Conclusion

The above description clearly explains what the find by id is and how it works in MongoDB to retrieve the documents according to the specified id by the user. As we know that the find() function is used in order to perform the task of retrieving the documents with the given id. The find() function internally calls the findOne() in order to handle the situation accordingly.

Recommended Articles

This is a guide to MongoDB find by id. Here we discuss the introduction, how does find by id work in MongoDB? and their examples respectively. You may also have a look at the following articles to learn more –

1. MongoDB Join
2. MongoDB findOne()
3. MongoDB Date Query
4. MongoDB Database