Nest.js, Graphql, Typeorm, Postgres mutations - postgresql

Question

I`m a newbee at this technologies and I literally dont understand how to do task. My task: create 2 tables, for categories and tasks, after that create mutation for creating category and tasks(todos).
mutation {
createTodo(input: {
categoryName: “”,
text: “”
}) {
category: {
id
title
}
id
text
isCompleted
}
}
I created objectTypes and input types, but I dont understand how to create such mutation. Example objectTypes and Inputs
#ObjectType()
export class CategoryType {
#Field(() => ID)
id: number
#Field(() => String)
readonly title: string
}
export interface TodoI {
id: number;
text: string;
isCompleted: boolean;
categoryId: number
category: any;
}
#InputType()
export class CategoryInput {
#Field()
readonly title: string
#Field(() => TodoInput,{nullable: true})
readonly todos: TodoI
}
#ObjectType()
export class TodoType {
#Field(() => ID)
id: number
#Field()
readonly text: string
#Field()
readonly isCompleted: boolean
#Field(() => Int)
readonly categoryId: number
}
#InputType()
export class TodoInput {
#Field()
readonly text: string;
#Field()
readonly isCompleted: boolean;
#Field(() => Int)
readonly categoryId: number;
}