# Data Structure Definition

In the previous chapter, the ServiceProvider got the path to a crud.yml told. This is where CRUDlex gets it’s information about what tables with what fields exists in your database. We will build up a valid, small example as we continue in this chapter.

## Entities

The first items in the crud.yml are the entities. Each entity is describing a single table with it’s fields. Let’s say we have two tables, libraries and books. So we define two entities with the same name. Note that this name is your choice, the table name of the database gets defined in a second.

    library:
    book:

In this case, the entities would be available under this URLs (assuming you mounted the Controller under “/crud”):

    http://.../crud/library
    http://.../crud/book

Now we declare the labels and the tables. The label is used for displaying links in the navigation and in some messages:

    library:
        label: Library
        table: library
    book:
        label: Book
        table: book

## Fields

So far, so good. In our minimal example, a library has a name and a Book has an author, a title and the amount of pages as fields.

    library:
        label: Library
        table: library
        fields:
            name:
                type: text
                label: Name
    book:
        label: Book
        table: book
        fields:
            author:
                type: text
                label: Author
            title:
                type: text
                label: Title
            pages:
                type: integer
                label: Pages

Note that the yml keys “name”, “author” and “title” directly name the database column names. Each one has a type and a label here. The type defines the database type and the label is used in various places to display the field. In this example, only simple string types are used and an integer for the book pages.

Beside this fields, the CRUDlex MySQL implementation assumes that you have some more fields per table:

- id int(11) NOT NULL AUTO_INCREMENT: the id of each row
- created_at datetime NOT NULL: a timestamp in UTC when the row was created
- updated_at datetime NOT NULL: a timestamp in UTC when the row was the last time updated
- deleted_at datetime DEFAULT NULL: defines when this entry was deleted in UTC. CRUDlex uses a soft delete mechanism hiding all rows where this is not null
- version int(11) NOT NULL: used for optimistic locking

See the CRUDlexSample.sql in the sample project for the exact table creation.