OctoberCMS Builder Plugin backend dropdown

Question

I would like to create a plugin where to create Posts, each post belong to 1 Category.

And there is a dropdown menu at the backend where you can choose which category the post belongs to when you are creating a post.

However, I want the the options in such dropdown depend on the model Category where the Value is category.name and Key is category.id instead of me typing the string into it.

Please help! Thanks

Thanks to Dragontree's suggestions: here is my 1st EDIT:

I already have my relationship set as followings:

in /models/Category.php

public $hasMany = [
    'posts' => ['stephenli\plugin\Models\Posts']
];

in /models/Post.php

public $belongsTo = [
    'category' => ['stephenli\plugin\Models\Category', 'key' => 'category_id']
];       /* I tried with or without  'key' => 'category_id'*/

and used relation widget at the Builder Plugin,

in /models/post/field.yaml

category_id:
    label: 'stephenli.postgod::lang.plugin.categorypick_label'
    oc.commentPosition: ''
    nameFrom: name
    descriptionFrom: description
    emptyOption: 'No categories found'
    span: auto
    type: relation

where in /models/post/columns.yaml

category_id:
    label: 'stephenli.plugin::lang.plugin.categorypick_label'
    type: text
    searchable: true
    sortable: true

When I access to my Post Plugin and click the Create button or try to amend any existing record in list, the following error shows:

Model 'plugin\Models\Post' does not contain a definition for 'category_id'.

Final edit:

To sum up everything for any other people who encounter the same issue in the future, there are two methods to solve the problem

You can either

1. Use Dropdown widget and change the options with detailed solution here provided by @Mittul At TechnoBrave
2. Or directly use Relation widget as provided in the suggested solution by @dragontree

Answer 1

There are several ways to define the dropdown options.

But in this case its sounds like you should be using the relation widget instead on a normal dropdown:

category:
    label: Category
    type: relation
    nameFrom: name 

PS. This also requires you to define the relations in the Post and Category models. But you should do that anyway.

It is also worth noting that the field name (in fields.yaml) should match the name of the relation.