Type System and Python Types

Before we dive deeper into how to use FastGraphQL to create and deploy your GraphQL API, it is important to look into the supported data types and how FastGraphQL connects python types with GraphQL Types.

Starting from the very beginning, let us look together into native python types.

Primitive Python Types

All primitive types are translated to GraphQL Scalar as displayed below

Python Type	GraphQL Scalar
`int`	`Integer!`
`bool`	`Boolean!`
`str`	`String!`
`float`	`Float!`

Note that all types are translated to non-null GraphQL types. If you would like to have nullable types, you should add Optional[...] in the declaration, as shown:

Python Type	GraphQL Scalar
`Optional[int]`	`Integer`
`Optional[bool]`	`Boolean`
`Optional[str]`	`String`
`Optional[float]`	`Float`

Extracting a more generic rule we can consider that:

Python Type	GraphQL Type
`T`	`T!`
`Optional[T]`	`T`

for any T being a supported type by FastGraqhQL

Lists

Assuming that T is any supported type, python lists are translated as follows:

Python Type	GraphQL Type
`List[T]`	`[T!]!`
`Optional[List[T]]`	`[T!]`
`List[Optional[T]]`	`[T]!`
`Optional[List[Optional[T]]]`	`[T]`

Dates, Times and Date-Times

FastGraphQL provides three custom GraphQL scalars with respective encoders and decoders to support date, time and date-time types.

Python Type	GraphQL Scalar	Default Format
`datetime.time`	`Time`	`%H:%M:%S`
`datetime.date`	`Date`	`%Y-%m-%d`
`datetime.datetime`	`DateTime`	`%H:%M:%ST%Y-%m-%d%z`

Date and Time format string

For all details about format strings please refer to strftime() and strptime() Format Codes

Date and Time format customization

The default format string can be customized. The details about it you can find under Global Customizations

Enums

Unfortunately, GraphQL Enums are yet not supported. I hope it will change soonish .