Entity headers are HTTP headers that provide information about the body of a message. They can appear in both requests and responses, describing properties of the content such as type, length, encoding, or last modification date.
1.
Content-Type
Content-Type: application/json; charset=UTF-8
2.
Content-Length
Content-Length: 1024
3.
Content-Encoding
Content-Encoding: gzip
4. Content-Language
Content-Language: de-DE
5. Cache-Location
Content-Location: /files/document.pdf
6. Last-Modified
Last-Modified: Tue, 30 Jan 2025 14:20:00 GMT
7. ETag
ETag: "abc123xyz"
8. Expires
Expires: Fri, 02 Feb 2025 12:00:00 GMT
9. Allow
Allow: GET, POST, HEAD
10. Refresh
(Not standardized but often used)
Refresh: 10; url=https://example.com
These headers help describe the content of an HTTP message, optimize caching strategies, and ensure correct rendering.
An Entity is a central concept in software development, particularly in Domain-Driven Design (DDD). It refers to an object or data record that has a unique identity and whose state can change over time. The identity of an entity remains constant, regardless of how its attributes change.
Unique Identity: Every entity has a unique identifier (e.g., an ID) that distinguishes it from other entities. This identity is the primary distinguishing feature and remains the same throughout the entity’s lifecycle.
Mutable State: Unlike a value object, an entity’s state can change. For example, a customer’s properties (like name or address) may change, but the customer remains the same through its unique identity.
Business Logic: Entities often encapsulate business logic that relates to their behavior and state within the domain.
Consider a Customer entity in an e-commerce system. This entity could have the following attributes:
If the customer’s name or address changes, the entity is still the same customer because of its unique ID. This is the key difference from a Value Object, which does not have a persistent identity.
Entities are often represented as database tables, where the unique identity is stored as a primary key. In an object-oriented programming model, entities are typically represented by a class or object that manages the entity's logic and state.