With the advent of micro services, many databases have become more manageable than at the start of the new millennium. Nevertheless, one is often faced with the task of understanding the structure of a database. Are there any foreign key relationships? Which of them have the ON DELETE CASCADE attribute? This is where the ER Diagrammer can show its strengths.
You connect to the corresponding database. The connection dialog is described in detail on the Hora page. You can create a diagram of the whole scheme. The tables in the diagram are clearly arranged: Independent tables can be found on the far left and the dependent tables on the right.
If the database has many tables, this overall view is not so helpful. It makes more sense to define subsets of tables that each represent a relevant partial aspect of the scheme and whose totality represents a coverage of the entire scheme. This is demonstrated below using our ZOO database as an example.
In most cases there are only a few central tables that are suitable for such a subset. What is the relationship between the enclosures (ENCLOSURE) and the keepers (KEEPER)? To understand this, a new subdiagram is created. In the adjacent dialog for the definition of this diagram, the table ENCLOSURE_KEEPER was selected with the option parent and child level 1. This selects the mesh of all parent and child tables of the selected table. For example, in a more realistic scheme, you could select two parent generations and three child generations, and you could manually add more tables to the selection.
The diagram name is Enclosure Keeper.
After clicking on the OK button you will see the adjacent picture. The relationships to the child table ENCLOSRE_KEEPER are colored red because an ON DELETE CASCADE is defined here.
After you have defined all relevant sub-diagrams in this way, you want to know which tables do not yet appear in any diagram. To do this, create another diagram and choose the Tables not covered by any diagram button at the bottom left of the screen. In this case we worked with parent and child level 1 again
The diagram name was Remaining Tables.
As a result you will see the adjacent picture. You can now be sure that your diagrams cover the entire scheme.
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Compare the ER Diagrammer with the feature list of competing products.