Data Modeling (AWS amplify, AppSync, GraphQL)

Before going to the data modeling we need to create the graphQL API.
Go to the link to create the graphQL API
This may looks time consuming. But if you're new to Data Modeling give it a shot. You're basic will be far more then clear.

Before start creating schema we've to know about some directives we're going to use while creating graphQL schema. And if don't have any idea about what GraphQL is then get some basic about GraphQl

Directives

@model @auth @hasOne @hasMany @belongTo @manyToMany @searchable @primaryKey and @index ....

@model

• Store objects in DynamoDB

• Configure CRUD resolvers

@auth

• API authorization strategies

@hasOne, @hasMany, @manyToMany, @belongsTo

• Create relationships between @model object types

@searchable

• Active search and sorting at the same time from database.

@primaryKey, @index

• Override default key property with custom data

Data Modeling

Now we're going to setup database tables using API(GraphQL)

Data types

1. Scalar type: title, content (Contains scalar value like ID, String, Int, Float, DateTime etc.)
2. Object type: Todo (which is a JavaScript Object)

Without @model directive, we'll not get any CRUD resolvers

1. @model

By adding @model directive we will get all the CRUD resolvers

Resolvers	Description
getTodo	Get one todo document using id or primaryKey
listTodo	Get all todo documents
createTodo	Insert one todo document
updateTodo	Update one todo document using id or primaryKey
deleteTodo	Delete one todo document using id or primaryKey

2. @auth

By adding @auth directive we will get the permission to use CRUD resolvers. Otherwise we might get an error about unauthorization.

createTodo, updateTodo, deleteTodo To create, update & delete a document in DB, we've to start the query with mutation

createTodo

• id: id is auto generated
• title: title comes from input object title field
• content: content comes from input object content field

getTodo, listTodo To get a document or all documents, the best practice is to start the query with query

getTodo

• id: Provide id to get a document from DB.
• title, content data will come from DB

listTodos

• id: Don't need id to get data
• title, content & other propertise will come from DB

deleteTodo

• id: Provide id to delete match document
• whole document object will delete from DB

3. @index

By using secondary index or @index directive we can create another extra queryField

• To use todoByTitleAndRank we've to provide title as argument in the query field
• To use todoByRank we've to provide rank as argument in the query field

Setup relationships between models

Directive	Data flow	Relationship	Example
@hasOne	One-directional	one-to-one	A project "has one" team
@hasMany	One-directional	one-to-many	A post "has many" comments
@belongsTo	Bi-directional	one-to-one or one-to-many	A project has one team or a team belongs to a project
@ManyToMany	Bi-directional	many-to-many	A blog has many tags and a tag has many blogs

4. @hasOne

• One-directional : We'll get child object inside of a parent object. Below here Child object is Team and Parent object is Project
• One-to-one : We'll get only one child inside of a parent object.

createTeam

• teamName: Provide team name

createProject

• projectName: Provide project name
• projectTeamId: Provide the exact same id of Team. This default field will be created and matched with the team id field & get the team data. We can override this field.

listProjects

• Team data will be found if projectTeamId === team.id.
• We'll get team data inside of project.
• But if we try to get project data inside of team it'll give us an error.

@hasOne(fields: ["fieldName"])

• This will override the default field (projectTeamId) by fieldName (teamID). We will not find the default field again.
• Now instead of matching projectTeamId === team.id, it is matching teamID === team.id.

5. @hasMany

• One-directional : We'll get array of child objects inside of a parent object. Below here Child object is Comment and Parent object is Post
• One-to-many : We'll get one or more child inside of a parent object.

createPost

• postName: Provide post title

createComment

• commentContent: Provide comment string
• postCommentsId: Provide the exact same id of Post. This default field will be created and matched with the Post id field & get the comment data. We can override this field.
• Adding another comment

listPosts

• Comments will be found if postCommentsId === post.id
• We'll get array of comment inside of post.
• But if we try to get post data inside of comments it'll give us an error.

@hasMany(indexName: "byPost", fields: ["id"])
postID: ID! @index(name: "byPost", sortKeyFields: ["content"]

• This will override the default field (postCommentsId) by property of index (postID). We will not find the default field again.
• Adding post
• Adding comment 1
• postID: Provide the exact same id of Post. This field will override the postCommentsId field and match the Post id field & get the comment data.
• Adding comment 2
• Now instead of matching postCommentsId === post.id, it is matching postID === post.id.

6. @belongsTo

• Bi-directional : We'll get array of child objects inside of a parent object & we'll also get parent inside of. Below here Child object is Comment and Parent object is Post
• Difference

Directive	Can be found child data inside parent object	Can be found parent data inside child object
@hasOne	Yes	No
@hasMany	Yes	No
@belongsTo	Yes	Yes

• I'm explaining @belongsTo directive for @hasMany relation. You should try out @belongsTo directive for @hasOne relation. There is no change in creating @hasOne and @hasMany schema and data table.Just we will find parent data inside of a child object.

createPost

• Provide postName

createComment

• Creating relation between two table by postCommentsId
• Add comment 2

listPost

• Getting child (comments) data inside parent (post) object
• Getting parent (post) data inside child (comments) object

@hasMany(indexName: "byPost", fields: ["id"])
postID: ID! @index(name: "byPost")

• This will override the default field (postCommentsId) by property of index (postID). We will not find the default field again. createPost
• Provide postName

createComment

• postID: Provide the exact same id of Post. This field will override the postCommentsId field and match the Post id field & get the comment data.
• Adding comment 2

listPost

• Getting child (comments) data inside parent (post) object
• Getting parent (post) data inside child (comments) object

7. @manyToMany

• This relation will create 3 data table.

Table	get	list	create	update	delete	subscription	Found Data Object
Post	Yes	Yes	Yes	Yes	Yes	Yes	Post, Tag, PostTags
Tag	Yes	Yes	Yes	Yes	Yes	Yes	Post, Tag, PostTags
PostTags	Yes	Yes	Yes	Yes	Yes	Yes	Post, Tag, PostTags

• Bi-directional : We'll get one table inside of another table.

createPost

• postName: Provide post name to create a post.

create Tag

• label: Provide label title to create a tag label.

createPostTags
postID: Use to provide post object.
tagID: Use to provide tag object.

Advanced

Create multiple relationships between multiple model

Relations between models are

• Department has one manager and many employees
• Manager has one department and many employees
• Employees has one department and one manager

createDepartment

• Provide Department name in the departmentName input
• We don't have manager and employee id. So we'll update the department later.

createManager

• Provide manager name in the managerName input
• Provide department id in the departmentID input.

createEmployee

• Provide employee name in the employeeName input
• Provide department id in the departmentID input.
• Provide manager id in the managerID input.
• And we're getting department and manager info in the Employee table

updateDepartment

• Provide selected department id in the id input
• Provide manager id in the managerID input
• and we're getting employee and manager info in department table.

listManagers

• And we're getting department and employee info in manager table.

That's it for now. Thanks for your patience. If this blog help you please give a react.
Next blog will be about filtering...

Comments

[Sumaiya176]

Waiting for next one 🤗

[Kamonchanok Foote]

Thank you so much, this article is very helpful.

[MD ARIFUL HASAN]

Welcome

[Zia]

Thanks,
I have a question, how to delete relations? ex. a Post has many tags, what if I want to remove a tag from a post?

[MD ARIFUL HASAN]

1st scenario:
If you want to remove a tag from posts you have to do deleteTag mutations.
deleteTag and give the tag id. That tag will remove from all the posts it's linked to.
2nd scenario:
If you want to delete a tag from a particular post you have to do updatePost mutations.

updatePost and provide the post id, then pass an empty string in the field where you provided the tag id to link post and tag.