What is an Entity Attribute?

An attribute is a characteristic of an entity object or view object, implemented as a JavaBean property of the object class. An attribute can correspond to a database column, or be independent of a column.

Two kinds of entity attributes

There are two kinds of entity attributes:

Attribute kind

Value derived from a database query?

Persisted in the database?

persistent

yes

yes (the value outlives the class that created it)

transient

no

no

Persistent entity attributes correspond to database columns

When you first create an entity object using reverse generation, a persistent entity attribute is created for each table column. After, if you change the table, you need to manually change the attribute.

For forward generation, when you create database tables from entity objects, each persistent attribute becomes a column in the table.

Entity attributes have settings

While creating or editing an entity object, you specify attribute settings. The settings can affect forward generation or the settings can be derived from an existing table (reverse generation). The following table summarizes what settings affect forward and reverse generation, and which settings apply to persistent and transient attributes.

Attribute Setting

Forward Generation

Reverse Generation

Persistent Attribute

Transient Attribute

Attribute Name

N/A

Default based on column name; you can change it to any Java identifier name.

Required

Required

Attribute Type

N/A

Default based on column data type; you can choose another type in the list.

Required

Required

Default Value

N/A

N/A

Optional

Optional

Primary Key

Becomes the table's primary key, or part of it if you specify multiple primary keys for a table (a composite key)

From the table; it must match the table.

Selectable

Selectable, but you should leave it deselected in most cases

Mandatory

Becomes a mandatory column in the table (a NOT NULL constraint is generated for that column in the table).

From the table; this value must match the table, or you might get problematic runtime behavior or an exception.

Selectable

Selectable

Persistent

Only persistent attributes are added to the table.

All attributes derived from the table are persistent; if you change it, this column does not get populated through the business components framework.

Selected

Deselected

Updateable

N/A

N/A

Selectable

Selectable

Refresh After

N/A

N/A except when the java.sql.type for this attribute is CHAR, then all Refresh After checkboxes are selected.

Selectable

N/A

Database Column Name

Becomes the table's column name

From the table; it must match the table.

Required; it must match the table.

N/A

Column Type

Becomes the table's column data type

From the table; it must match the table.

Required; it must match the table.

N/A

Queriable

N/A

N/A

Selectable

N/A

Unique

If selected, the column has a unique constraint.

From the table; it must match the table.

Selectable

N/A

Change Indicator

N/A

N/A

Selectable

N/A

In general, if you are performing reverse generation, you don't want to change the primary key, mandatory, database column name, column type, and unique settings that were received from the table. For forward generation, the primary key, mandatory, persistent, database column name, column type, and unique settings are used to generate tables.

Entity attributes are based on the UML definition

In Business Components for Java, the term "attribute" is based on the UML definition, not the XML definition. In UML, an attribute is a named property of a class that describes a range of values that instances of that class might hold.

Attribute kind	Value derived from a database query?	Persisted in the database?
persistent	yes	yes (the value outlives the class that created it)
transient	no	no

Attribute Setting	Forward Generation	Reverse Generation	Persistent Attribute	Transient Attribute
Attribute Name	N/A	Default based on column name; you can change it to any Java identifier name.	Required	Required
Attribute Type	N/A	Default based on column data type; you can choose another type in the list.	Required	Required
Default Value	N/A	N/A	Optional	Optional
Primary Key	Becomes the table's primary key, or part of it if you specify multiple primary keys for a table (a composite key)	From the table; it must match the table.	Selectable	Selectable, but you should leave it deselected in most cases
Mandatory	Becomes a mandatory column in the table (a NOT NULL constraint is generated for that column in the table).	From the table; this value must match the table, or you might get problematic runtime behavior or an exception.	Selectable	Selectable
Persistent	Only persistent attributes are added to the table.	All attributes derived from the table are persistent; if you change it, this column does not get populated through the business components framework.	Selected	Deselected
Updateable	N/A	N/A	Selectable	Selectable
Refresh After	N/A	N/A except when the java.sql.type for this attribute is CHAR, then all Refresh After checkboxes are selected.	Selectable	N/A
Database Column Name	Becomes the table's column name	From the table; it must match the table.	Required; it must match the table.	N/A
Column Type	Becomes the table's column data type	From the table; it must match the table.	Required; it must match the table.	N/A
Queriable	N/A	N/A	Selectable	N/A
Unique	If selected, the column has a unique constraint.	From the table; it must match the table.	Selectable	N/A
Change Indicator	N/A	N/A	Selectable	N/A