Core Concepts

Understanding DynamoDB's core concepts is essential before you start building. This lesson covers tables, items, attributes, primary keys, and data types — the fundamental building blocks of every DynamoDB application.

---

Tables

A table is the top-level container for data in DynamoDB, similar to a table in a relational database:

• Each table has a name that must be unique within an AWS account and Region
• Tables are schemaless — only the primary key attributes must be defined upfront
• Non-key attributes can vary from item to item
• There is no practical limit on the number of items a table can store
• Table storage grows automatically as you add data

---

Items

An item is a single record in a table, similar to a row in a relational database:

• Each item is uniquely identified by its primary key
• An item is a collection of attributes
• Maximum item size is 400 KB (including attribute names and values)
• Items in the same table can have completely different attributes

Example Items in a Users Table

{
  "UserId": "user-001",
  "Name": "Alice",
  "Email": "alice@example.com",
  "Age": 30
}

{
  "UserId": "user-002",
  "Name": "Bob",
  "Phone": "+44-7700-900000",
  "Address": {
    "City": "London",
    "Postcode": "SW1A 1AA"
  }
}

Notice that Alice has Email and Age while Bob has Phone and Address — this is perfectly valid.

---

Attributes

An attribute is a named data element within an item, similar to a column in a relational database:

• Each attribute has a name and a value
• Attribute names are strings
• Attributes can be top-level or nested (up to 32 levels deep)

---

Data Types

DynamoDB supports three categories of data types:

Scalar Types

Type	Code	Description	Example
String	S	UTF-8 text	"Hello World"
Number	N	Numeric (integer or float)	42, 3.14
Binary	B	Base64-encoded binary data	"dGVzdA=="
Boolean	BOOL	True or false	true
Null	NULL	Null value	true (the value of the NULL type)

Document Types

Type	Code	Description	Example
List	L	Ordered collection (like a JSON array)	["red", "green", "blue"]
Map	M	Unordered key-value pairs (like a JSON object)	{"City": "London"}

Set Types

Type	Code	Description	Example
String Set	SS	Set of unique strings	["admin", "editor"]
Number Set	NS	Set of unique numbers	[1, 2, 3]
Binary Set	BS	Set of unique binary values	["dGVzdA=="]

Tip: Sets must contain elements of the same type, and all elements must be unique. Empty sets are not allowed.

---

Primary Keys