> For the complete documentation index, see [llms.txt](https://docs.langstack.com/welcome/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.langstack.com/welcome/get-started/learn-langstack/introduction-to-entities/fields.md).

# Fields

* A field is the building block of an Entity that stores a single type of data. When the Entity is created, each field becomes a column in the Entity.
* The fields define the type of data to be stored, its accessibility, readability, and generation methods.
* A field comprises the following details:
  1. Field Name: Label of the field, i.e., the title of the column. This must be unique.
  2. Data Type: Defines the data type or another entity for the information to be stored in this field.
  3. Default Value: Defines the default value to be displayed. A field must have at least one (1) default value.
  4. Primary: Defines field as the primary key. A primary key is a unique key used as a reference point for entities to relate and connect.
  5. Unique: Defines field as unique.
  6. Not Empty: Defines the field to be non-empty, which means it must have some value.
  7. Read Only: Defines field as read-only, which means that though data can be entered into it, it cannot be edited or updated.
  8. Auto Increment: Defines field as auto-incremented, which means the field for this number will be incremented with the addition of data or record. When this element is selected, it activates the Start field.
  9. Start: Defines the starting number Auto Increment.
  10. List: Defines a field to contain values as a list.
  11. Default Field: Defines a field to be shown as the default field.
  12. Display: Defines the field to be displayed and not hidden.

![](/files/09fsNcVfpngdDlIFoDxf)

13\. Auto Generate: If the data type is selected as GUID, the field “Auto Generate” displays. Selecting this field defines that a number will automatically be generated for this field when a record is added.

{% embed url="<https://media.langstack.com/documentation/media/images/code/training_manual/chapter_5/ch5autogenfield.png>" %}