Develop Your First Java Application in 20 Minutes › Project Entity and Triples › Use Inheritance to Define Field Properties

Use Inheritance to Define Field Properties

You can define properties to the fields in an entity. Properties provide information about the type of data each field stores.

To define the properties of Project’s fields

1. Click the Show/Hide Library Objects button to display the library objects.
2. Click the Fields button to display field objects to ensure that the Object Browser is focused on fields.
3. Select the Project ID field in the Object Browser by clicking the name (not the icon to the left of the name) and drag the field from the Object Browser to the source object box of the Model Editor.

   This changes the Model Editor source object type to Field, and changes the verb list so that only verbs appropriate for fields are contained in it.

   Note: The cursor changes to a closed parcel icon when you drag an object. It changes to an open parcel icon when it is over a location where you can drop the object:

   The following table shows the closed and open parcel icons:

1. From the verb list, select is a FLD.
2. From the Object Browser, drag the library object FIELDS/Identifier field to the target object box, and press Enter.

   Note: You have to scroll down the Object Browser to find the FIELDS/Identifier field. You can use the filter box at the top of the Object Browser to only show some of the library items. In this case, you could type *Identifier* to display only FIELDS/Identifier. Remember to set the filter back to * when you are done.

   You just created the triple Project ID is a FIELDS/Identifier.

   Click the Refresh button on the Object Browser.

   The Project ID field has a plus sign (+) to the left, indicating that it now has scoped objects.

3. Click the plus sign (+) to expand the field:

   

   You can see that Project ID now has the value *Blank, but you cannot tell much else about what it inherited from FIELDS/Identifier. Values are another type of CA Plex object.

4. Drag the Project ID field from the Object Browser to the body of the Model Editor. The body is the bottom part of the editor, where the full triples are displayed.

   When you drag one or more objects to the body of the Model Editor, the display changes to show you only the triples that define those objects. This is called focusing the Model Editor. When you drag the Project ID field to the Model Editor, it focuses on this field, showing the triple Project ID is a FIELDS/Identifier. This still does not give you much information.

5. Click the Two Levels toolbar button to see more about what an object inherits from its ancestor objects.

   The Model Editor shows another level of detail.

   

   Now you can see that Project ID has inherited a data type of character and length of 10, along with the value *Blank (which you saw in the Object Browser in Step 7).

   Note: In Step 5, you dragged the library object FIELDS/Identifier from the Object Browser to the target object box in the Model Editor. You can enter the name of the object into the target object box (without the library name) to accomplish the same thing. In Step 5, you would have entered Identifier.

Important! If you entered a wrong object name, you could create a new object with the wrong name. If this happens, find the erroneous object in the Object Browser and delete it, selecting the Ripple Delete check box on the Delete dialog.

1. Click the One Level toolbar button to set the Model Editor to show a single level of information.
2. Reset the Model Editor display by clicking the Clear Focus button.

   All of the triples appear in the model again.

   

   Note: If your Model Editor displays many more triples than shown in the previous graphic, then you have your model set to display library objects. If this is the case, click the Show/Hide Library Objects toolbar button.

3. Drag the Project Description field from the body of the Model Editor to the source object box. This field is in the third column of the Project has Project Description triple.
4. Enter ShortDescription in the target object box, and press Enter.

   The Model Editor displays the triple as:

   Project Description is a FIELDS/ShortDescription

   This indicates that you correctly spelled the name of the pattern library field.

   Note: If you create a new object for a model, and it happens to share the name of a library object, you must rename your object or delete it (if you did not intend to create it).

5. Repeat either Steps 3 to 5 or Steps 12 to 13 to create the following triples:

   Project Start Date is a DATE/CheckedDateISO
   Project End Date is a DATE/CheckedDateISO

   Project Description Length NBR 255

6. Click the Refresh toolbar button (on the main toolbar, not on the Object Browser).

   Your Model Editor should look like this:

   

   Inheriting from DATE/CheckedDateISO gives the fields functionality to ensure that end users enter valid dates.

7. Use the process explained in Steps 8 and 9 to look at the characteristics that these fields inherit from the pattern library fields.