Incomputer programming,create, read, update, and delete (CRUD) are the four basic operations (actions) ofpersistent storage.[1] CRUD is also sometimes used to describeuser interface conventions that facilitate viewing, searching, and changing information using computer-basedforms andreports.
The termC.R.U.D was likely first popularized in 1983[2] byJames Martin in his bookManaging the data-base environment.
Data can be put in alocation/area of a storage mechanism.
Together these four operations make up the basic operations of storage management known as CRUD:Create,Read,Update andDelete.
The acronym CRUD refers to the major operations which are implemented bydatabases. Each letter in the acronym can be mapped to a standardStructured Query Language (SQL) statement.[3]
| CRUD | SQL |
|---|---|
| Create | INSERT |
| Read | SELECT |
| Update | UPDATE |
| Delete | DELETE |
Althoughrelational databases are a commonpersistence layer in software applications, numerous other persistence layers exist. CRUD functionality can for example be implemented withdocument databases,object databases,XML databases, text files, or binary files.
Somebig data systems do not implement UPDATE, but have only a timestamped INSERT (journaling), storing a completely new version of the object each time.
The acronym CRUD also appears in the discussion ofRESTful APIs. Each letter in the acronym may be mapped to aHypertext Transfer Protocol (HTTP) method:
| CRUD | HTTP |
|---|---|
| Create | POST, PUT if we don't have `id` or `uuid` |
| Read | GET |
| Update | PUT to replace,PATCH to modify |
| Delete | DELETE |
In HTTP, the GET (read), PUT (create and update), POST (create - if we don't have `id` or `uuid`), and DELETE (delete) methods are CRUD operations as they have storage management semantics, meaning that they letuser agents directly manipulate the states of targetresources.[4] ThePOST method, on the other hand, is a process operation that has target-resource-specific semantics which typically exceed the scope of CRUD operations.[5]
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CRUD is also relevant at the user interface level of most applications. For example, in address book software, the basic storage unit is an individualcontact entry. As a bare minimum, the software must allow the user to:[6]
Because these operations are so fundamental, they are oftendocumented and described under one comprehensive heading such as "contact management" or "document management" in general.[citation needed]
Other variations of CRUD include:
POST only becomes an issue when it is used in a situation for which some other method is ideally suited: e.g., retrieval of information that should be a representation of some resource (GET), complete replacement of a representation (PUT), or any of the other standardized methods that tell intermediaries something more valuable than "this may change something." The other methods are more valuable to intermediaries because they say something about how failures can be automatically handled and how intermediate caches can optimize their behavior. POST does not have those characteristics, but that doesn't mean we can live without it. POST serves many useful purposes in HTTP, including the general purpose of "this action isn't worth standardizing."
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