Enumerations

Enumerations

Enumeration is a special data type describing some limited collection of items that is static or pseudo-static (changing very rare). Enumerations are used as a one of data types of entity attributes.

Enumerations differ from entities by following reasons

• They have static (or pseudo-static) list of values
• They don't have many different values (usually from 2-3 to 10-15 different values)
• Their values can be hardcoded and used in algorithms (i.e. write code like client.gender = Gender.Male), while using entity record references (i.e. code like client.product_id = 2) is a bad idea

Good examples of enumerations are

• Gender (male \ female)
• Monthes of the year (Jab,Feb,March etc.)
• Programming languages (Java, C, PHP etc.)

Bad examples of enumerations are

• Products (because list of products can be changed very often)
• Car models (same reason, we see that every year new car models appear and it would be hard to support code directly referencing certain car model)

Enumeration storage

There are 2 types of enumerations from the storage point of view

Inline

Inline enumerations are not stored in a separate table. Enumeration value is stored directly in a table column. In that case table column has a type of enumeration value (for example, String).

Pseudo code example

    create table SBT_CLIENT
    (
       ID int,
       NAME varchar(255),
       GENDER char(1)
    )

In this example column GENDER has a enumeration type Gender which values (M or F) are stored directly in a table

ID	NAME	GENDER
1	John Smith	M
2	Ted Frank	M
3	Mary Thompson	F

Stored

Stored enumeration values are stored in a separate tables, and are referenced by other table records by their primary key

    create table SBT_GENDER
    (
       ID int,
       CODE char(1),
       NAME varchar(10)
    )

    create table SBT_CLIENT
    (
       ID int,
       NAME varchar(255),
       GENDER_ID int
    )

In this example column GENDER_ID has a enumeration type Gender which values (M or F) are stored in a table SBT_GENDER

ID	CODE	NAME
1	M	Male
2	F	Female

And SBT_CLIENT values in that case are

ID	NAME	GENDER_ID
1	John Smith	1
2	Ted Frank	1
3	Mary Thompson	2