Entities and Objects: Description of Objects: Relation

For technical specifications on relations between tables, see the official documentation of PostgreSQL.

Regarding the creation and use of the relations, has already been given full explanation in paragrafici earlier.

The window shown in the figures below, lets you change the properties of an object relation.

As with all objects in a project, the area has a window where you must enter the name of the object, unique within the same project. The window is made up of two folders, grouping in the different logical characteristics of the object.

In Folder "Topics" are three lists. The list left lists all fields in the source table (or father), while the list on the right lists all the fields in the destination table (or daughter), in central list can be found all relations field / field between the two tables. To establish a relation between two tables must be selected in each of these areas to be connected, and press the button at the top left of the central list (identified with a "+"); this field will be selected to populate the list of relations in the central list. It is not possible to create a relation without having at least one item. To delete a row from the list is central to press the button on the upper-right (identified with a "-").

The combo under the three lists are used by PostgreSQL, and determine the type of relation between the two tables, and the definition of this type of relation conditions graphical representation of a line linking within the diagram, in order to facilitate the identifying and understanding the type of relation.

The last folder, exist in almost all the windows on object-oriented database, appear SQL commands on the building and the construction of instruction takes place in real time, and depends on the settings in the property contained in the current window.