Primary Keys

In the native AWS DynamoDB API primary keys are represented in two different ways depending on context:

AWS	Example	Context
Primary Keys	{"id": "1", "year": 2023}	GetItem, PutItem, DeleteItem AWS API
Key Condition Expressions	#id=:val1 and #year > :val2	Query AWS API

Here we see that for CRUD operations the primary key is represented as a JSON object where each value is checked for equality, while for Query operations the primary key is represented as a key condition expression .

The High Level API unifies the two different ways to represent a primary key into a single type safe API.

Unified Type Safe High Level API for Primary Key Expressions

Assuming the below model

final case class Person(id: String, year: Int, address: String)
object Person {
  implicit val schema: Schema.CaseClass3[String, Int, String, Person] = DeriveSchema.gen[Person]
  val (id, year, address) = ProjectExpression.accessors[Person]
}
final case class Employee(id: String, group: String, address: String)
object Person {
  implicit val schema: Schema.CaseClass3[String, Int, String, Person] = DeriveSchema.gen[Person]
  val (id, year, address) = ProjectExpression.accessors[Person]
}

The High Level API unifies the two different ways into a single Type Safe API that is accessed by using the ProjectExpression returned by the ProjectExpression.accessors function as a springboard via the partitionKey and sortKey methods.

AWS	Example	Context
Primary Keys	Person.id.partitionKey === "1" && Person.year.sortKey === "2020"	GetItem, PutItem, DeleteItem
Key Condition Expressions	[Query].whereKey(Person.id.partitionKey === "1" && Person.year.sortKey > 2020)	[Query].whereKey

Valid operations on primary keys are:

context	operation	applies to
Person.id.partitionKey Person.year.sortKey	===	GetItem, PutItem, DeleteItem, [Query].whereKey
Person.id.partitionKey === "1"	&&	GetItem, PutItem, DeleteItem, [Query].whereKey. Provides conjunction from a partition key to a sort key
Person.year.sortKey	>	[Query].whereKey only
	>=
	<
	<=
	<>
	.between(2021, 2023)
Employee.group.sortKey	.beginsWith("Group1")	Applies to String sort keys only