MongoDB CRUD

MongoDB CRUD #

Let's learn about how to perform CRUD operations in MongoDB.

## Create - Create Operation(Insert)

Create is the operation of creating or adding new documents to a collection. In MongoDB, create operations are performed through inserts. If a collection does not exist, the insert command will create a new collection.

MongoDB provides the following two insert methods:

• db.collection.insertOne()
• db.collectioin.insertMany()

---

insertOne() #

First, db.collection.insertOne() is a command to insert a single document into a collection.

// Inserting one document
db.collection.insertOne({ key: "value" });

If the insert is successful, it returns the _id of the inserted document.

insertMany() #

db.collection.insertMany() is a command to insert multiple documents into a collection.

This command is used to insert multiple documents.

// Inserting multiple documents
db.collection.insertMany([
  { key1: "value1" },
  { key2: "value2" }
]);

insertMany takes an array as input to insert data into the table, and the returned _id is also in array form.

Read - Read Operation(Find) #

Read performs the operation of reading documents from a collection. This operation is carried out using the find function.

find() can read documents using query filters.

db.collection.find({}) // 전체 조회
db.collection.find( { size: { h: 14, w: 21, uom: "cm" } }) // 쿼리 필터 적용

Executing the find function returns the _id and document; if none are found, it returns nothing.

When searching for documents using query filters, i.e., conditions, you can use fields and nested fields together.

db.collection.find({ "size.uom": "in" })

Although an example is not provided here, you can also search for data using operators.

### Retrieving Only Necessary Data The `find` operation above generally retrieves all data of a document, including its `_id`. However, if you want to retrieve only specific fields, you can do so as follows.

db.collection.find({조건}, {가져올필드 : 1})
db.collection.find( { size : { h: 14, w: 21, uom: "cm"} }, { item: 1 } )
db.collection.find( { size : { h: 14, w: 21, uom: "cm"} }, { _id: 0, item: 1 } ) // 아이디 필드는 제외하고 가져옴

In the example above, only the item field of the collection matching the size condition is retrieved.

If you specify 0, you can exclude a field from being retrieved.

Querying Array Conditions #

You want to query using a data field where a specific field's value is an array. It's convenient to think of it as an "IN clause."

However, if you simply put an array in the condition clause of find, the data can only be retrieved if the order matches exactly.

Therefore, if you want to input conditions regardless of order, you can do so as follows.

db.collection.find( { 필드 : { &all : [데이터1, 데이터2] } } )

Comparison operators and logical operators also exist in MongoDB, which I will explore later. Additionally, there are Cursor queries and null-related handling, which I'll cover later!

Update - Update Operation(Update, Replace) #

Update is the operation for modifying documents in a collection.

• db.collection.updateOne()
• db.collection.updateMany()
• db.collection.replaceOne()

updateOne() modifies a single document. When updating, you specify the document to modify using conditions; if multiple documents are found, it modifies the first one.

db.collection.updateOne(
	{ item: "name" },
	{
		$set: {"size.uom": "cm", status: "P"},
		$currentDate: { lastModified: true }
	}
)

updateMany() is used to modify many documents at once, and its usage is the same as updateOne.

db.collection.updateMany(
	{ item: "name" },
	{
		$set: {"size.uom": "cm", status: "P"},
		$currentDate: { lastModified: true }
	}
)

All the update operations above updated field values using $set. replaceOne(), unlike the other update methods, replaces the document with the provided arguments.

db.collection.replaceOne(
	{ item: "paper" },
	{ item: "paper", instock" [ 업데이트할 필드 ]}
)

Delete - Delete Operation(Delete) #

Delete is the operation for removing documents from a collection.

• db.collection.deleteOne()
• db.collection.deleteMany()

deleteMany() deletes multiple documents. Specifying conditions is similar to find. To delete all, use {}.

db.collection.deleteMany({}) // 전체 삭제
db.collection.deleteMany({조건: 조건})

deleteOne() is similar to the above but deletes the first document found.