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GraphQL–DotNet–Nullability

In GraphQL all types are nullable by default. In the first version of GraphQL non-null fields were even not supported at all(!).

There is a good reason for this; evolvability of your API. Non-nullable fields make it hard to change your contract. Switching from a non-nullable to a nullable field will always be a breaking change. This explains why GraphQL makes every type nullable by default, and you have to explicitly mark a field as non-null by adding the bang character (!) to your schema definition.

When you are using GraphQL.NET, the principles above still apply but the library follows some different rules to mark a field as nullable or not. For structs (integers, booleans, …) GraphQL.NET will mark them as not-null by default. You even have to explicitly mark them as nullable(see this post: https://bartwullems.blogspot.com/2018/11/graphqldotnetnullable-types-nullable.html). For all other types the rules above are followed and every type is nullable by default.

If you don’t want this, you have to wrap your GraphQL.NET type in a NonNullGraphType wrapper.

Here is a example for a single type:

This will generate the following schema:

And also an example for a list:

This will generate the following schema:

More information:

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