DynamoDB CRUD Operations

CRUD stands for Create, Read, Update, and Delete — the four fundamental operations you perform on any database. In DynamoDB, each operation has a dedicated API call with its own rules and behavior. This topic walks through each one with clear examples.

Overview of CRUD in DynamoDB

DynamoDB also provides BatchWriteItem and BatchGetItem for handling multiple items in one API call.

Create: PutItem

PutItem writes a complete item into the table. If an item with the same primary key already exists, PutItem replaces it entirely.

Example Scenario

A hospital app needs to register a new patient. The table is Patients with PatientID as the partition key.

PutItem Request:
{
  "TableName": "Patients",
  "Item": {
    "PatientID":   { "S": "P1001" },
    "Name":        { "S": "Meera Nair" },
    "Age":         { "N": "45" },
    "BloodGroup":  { "S": "O+" },
    "WardNumber":  { "N": "12" }
  }
}

DynamoDB stores this item on the partition that matches the hash of P1001.

Warning: PutItem Overwrites

If you run PutItem again with PatientID: P1001 but different attributes, DynamoDB replaces the entire previous item with the new one. Use UpdateItem instead when you want to change only a few attributes without touching the rest.

Read: GetItem

GetItem retrieves exactly one item using its full primary key. It is the fastest read operation in DynamoDB because it goes directly to the exact partition where the item lives.

Example

GetItem Request:
{
  "TableName": "Patients",
  "Key": {
    "PatientID": { "S": "P1001" }
  }
}

Response:
{
  "Item": {
    "PatientID":  { "S": "P1001" },
    "Name":       { "S": "Meera Nair" },
    "Age":        { "N": "45" },
    "BloodGroup": { "S": "O+" },
    "WardNumber": { "N": "12" }
  }
}

Projection Expressions

If you only need certain attributes, specify them using a Projection Expression. This reduces the amount of data DynamoDB returns and lowers your read cost.

ProjectionExpression: "Name, BloodGroup"

Response (only requested fields):
{
  "Name":       { "S": "Meera Nair" },
  "BloodGroup": { "S": "O+" }
}

Update: UpdateItem

UpdateItem modifies one or more attributes of an existing item without touching the attributes you do not mention. This makes it safer than PutItem for partial edits.

Update Expressions

DynamoDB uses an Update Expression to describe the change. The most common actions are:

• SET — adds or updates an attribute
• REMOVE — deletes an attribute from the item
• ADD — increments a number or adds to a set
• DELETE — removes elements from a set

Example: Update Ward Number

UpdateItem Request:
{
  "TableName": "Patients",
  "Key": {
    "PatientID": { "S": "P1001" }
  },
  "UpdateExpression": "SET WardNumber = :newWard",
  "ExpressionAttributeValues": {
    ":newWard": { "N": "7" }
  }
}

Only the WardNumber attribute changes. Name, Age, and BloodGroup remain exactly as they were.

Atomic Counter: Increment a Number

UpdateExpression: "ADD ViewCount :inc"
ExpressionAttributeValues: { ":inc": { "N": "1" } }

This safely increments ViewCount by 1 even if multiple users trigger it simultaneously, because DynamoDB handles it atomically.

Delete: DeleteItem

DeleteItem removes a single item from a table using its primary key. If the item does not exist, DynamoDB performs the operation successfully without throwing an error.

Example

DeleteItem Request:
{
  "TableName": "Patients",
  "Key": {
    "PatientID": { "S": "P1001" }
  }
}

Patient P1001 is permanently removed from the Patients table.

Batch Operations

BatchGetItem

Retrieves multiple items from one or more tables in a single API call. You can fetch up to 100 items at once. Each item still requires its full primary key.

BatchGetItem fetches P1001, P1002, and P1003 in one round trip
instead of three separate GetItem calls.

BatchWriteItem

Puts or deletes up to 25 items in a single call. You cannot update items using BatchWriteItem — use UpdateItem for updates. BatchWriteItem is ideal for loading bulk data.

Diagram: CRUD Flow for a Delivery App

TABLE: Deliveries  (PartitionKey: DeliveryID)

Step 1 — PutItem:    Add new delivery D500 (Status: "Pending")
          ↓
Step 2 — GetItem:    Driver fetches D500 details
          ↓
Step 3 — UpdateItem: SET Status = "Out for Delivery"
          ↓
Step 4 — UpdateItem: SET Status = "Delivered", DeliveredAt = timestamp
          ↓
Step 5 — DeleteItem: Archive job — remove D500 after 30 days

Return Values

DynamoDB can return the item's data before or after an operation, using the ReturnValues parameter:

• NONE — Return nothing (default)
• ALL_OLD — Return the item as it was before the operation
• ALL_NEW — Return the item as it is after the operation
• UPDATED_OLD — Return only the changed attributes before the update
• UPDATED_NEW — Return only the changed attributes after the update

Summary