Fields

Data is stored in Polybase in the form of contracts. Each contract in turn defines the shape and structure of the data itself using fields.

Field declarations must appear at the beginning of the contract declaration. In addition, each contract must have a unique field declaration of the form:

id : string;

This field is used as the unique identifier for a record (an instance) of the contract. Currently, the id field is only allowed to be of type string, but this restriction may be lifted in the future.

Required fields

By default, all fields in the contract are required. Required fields are usual field declarations. For instance:

contract Person {
    name: string;
    age: number;
    salary: number;
    qualified: boolean;
 
    ...
}

Optional fields

In addition, Polylang also allows fields to be declared as optional. This is done by adding a ? to the field name:

contract Employee {
    employed?: boolean;
    balanceDetails?: number;
 
    ...
}

Nested Fields

Field declarations can also be nested. This is useful when the field itself is of composite nature (meaning that the sub-fields within this field are all related in some sense). For example:

contract Person {
    id: string;
    name: string;
    address: {
        street: string;
        city: string;
        country: Country;
    }
 
    ...
 }
 
contract Country {
    id: string;
    name: string;
    countryCode: number;
 
    ...
}

In the example above, the address field is a composite field consisting of sub-fields, one of which is a contract type itself (Country).