Document System Tutorial Part 5 - Linking Models (Documents)
============================================================
In this part, we will talk about linking models using a foreign key for documents.

Let’s create a new file in the models folder named **channel.go** with the following codes below:

.. code-block:: go

    package models

    import (
        "github.com/uadmin/uadmin"
    )

    // Channel !
    type Channel struct {
        uadmin.Model
        Name string `uadmin:"required"`
    }

Create another file in the models folder named **document.go** with the following codes below. Link the Channel model to the Document model.

.. code-block:: go

    package models

    import (
        "time"

        "github.com/uadmin/uadmin"
    )

    // Document !
    type Document struct {
        uadmin.Model
        Name        string
        File        string `uadmin:"file"`
        Description string `uadmin:"html"`
        RawText     string `uadmin:"list_exclude"`
        Folder      Folder `uadmin:"filter"`
        FolderID    uint
        CreatedDate time.Time
        Channel     Channel `uadmin:"list_exclude"`
        ChannelID   uint
        CreatedBy   string
    }

**file** tag allows the user to upload a file from your computer.

**html** tag allows the user to modify text in HTML format.

**list_exclude** tag hides the field or column name in the model structure.

**filter** tag adds a field in the uAdmin filter feature to search based on the related field.

**CreatedBy** field is a reserved word in uAdmin used to display the name of the user who created the record in the model.

And of course, let's create permissions to the group and user who can access the specific document.

**document_group.go**

.. code-block:: go

    package models

    import (
        "github.com/uadmin/uadmin"
    )

    // DocumentGroup !
    type DocumentGroup struct {
        uadmin.Model
        Group      uadmin.UserGroup
        GroupID    uint
        Document   Document
        DocumentID uint
        Read       bool
        Add        bool
        Edit       bool
        Delete     bool
    }

    // DocumentGroup function that returns string value
    func (d *DocumentGroup) String() string {

        // Gives access to the fields in another model
        uadmin.Preload(d)

        // Returns the GroupName from the Group model
        return d.Group.GroupName
    }

**document_user.go**

.. code-block:: go

    package models

    import (
        "github.com/uadmin/uadmin"
    )

    // DocumentUser !
    type DocumentUser struct {
        uadmin.Model
        User       uadmin.User
        UserID     uint
        Document   Document
        DocumentID uint
        Read       bool
        Add        bool
        Edit       bool
        Delete     bool
    }

    // DocumentUser function that returns string value
    func (d *DocumentUser) String() string {

        // Gives access to the fields in another model
        uadmin.Preload(d)

        // Returns the full name from the User model
        return d.User.String()
    }

What if the user updates something in the document then reuploads it? In this situation, let's create a file named **document_version.go**. Every updates done by the user, the version number of the document will change.

.. code-block:: go

    package models

    import (
        "fmt"
        "time"

        "github.com/uadmin/uadmin"
    )

    // DocumentVersion !
    type DocumentVersion struct {
        uadmin.Model
        Document   Document
        DocumentID uint
        File       string `uadmin:"file"`
        Number     int    `uadmin:"help:version number"`
        Date       time.Time
    }

    // Returns the version number
    func (d DocumentVersion) String() string {
        return fmt.Sprint(d.Number)
    }

**help** tag notifies the user to give solutions to advanced tasks.

Now go to main.go and register the models that we have created.

.. code-block:: go

    func main() {
        // Register models to uAdmin
        uadmin.Register(
            models.Folder{},
            models.FolderGroup{},
            models.FolderUser{},
            models.Channel{}, // place it here
            models.Document{}, // place it here
            models.DocumentGroup{}, // place it here
            models.DocumentUser{}, // place it here
            models.DocumentVersion{}, // place it here
        )

        // Some codes
    }

Run your application. As expected, Channels and Document related models are added in the uAdmin Dashboard.

.. image:: assets/fivemodelscreated.png

|

Click `here`_ to view our progress so far.

In the `next part`_, we will discuss about document concepts and how to create records in an application.

.. _here: https://uadmin-docs.readthedocs.io/en/latest/document_system/tutorial/full_code/part5.html
.. _next part: https://uadmin-docs.readthedocs.io/en/latest/document_system/tutorial/part6.html

.. toctree::
   :maxdepth: 1

   full_code/part5