8.5.3 Refactoring metamodels with XML
Most refactoring operations on the metamodels can be carried
out simply with the existing metamodeling tools. For instance, renaming a type
in the Object Tool is sufficient, with no need to manually update other parts of
the metamodel that use that type (generators excepted). There are however
sometimes specific operations or mass refactorings that would be easier or
indeed only possible with XML. These can be accomplished by exporting the
metamodel to an MXT file, modifying the file, and re-importing
it.
Moving a property slot to a supertype
 | As
of MetaEdit+ 5.6, this can now be accomplished directly in the metamodeling
tools with Refactor | Push Up Property (see Section 2.1.3, Refactor types). The old instructions
below have been left, as they may form a useful basis for understanding how to
use MXT for more complicated
options. |
In the metamodeling tools,
deleting a property slot from a subtype and then adding a similar one to the
supertype — as separate operations — will result in a new property
slot, losing any existing values of that property in instances of the subtype.
That is no problem when building the metamodel initially (no valuable instances
will exist yet), but in the less common case of a major metamodel refactoring
with existing models, it is good to have a solution that preserves all values.
With careful MXT use, we can push the existing slot up into the supertype and
maintain existing property values.
Export the metamodel to an MXT file, and edit it to
produce two new files:
 | propertyRemovedFromSubtype.mxt,
with the property slot cut from the
subtype |
| propertyAddedToSupertype.mxt,
with the property slot pasted to the desired position in the supertype’s
list of slots |
The slot should include the
<slot> tag and all its contents
up to and including the closing of the
slot tag. It is important that the
internal slot id is the same as in the initial file. Normally the property type,
typeName and local name should also be unchanged.
Logout and take a backup of your repository, as before any
major operation.
| 1) | Select
no projects and
Login |
| 2) | Switch
to the Type Browser
tab |
| 3) | Repository
| Import, and select
propertyRemovedFromSubtype.mxt |
| 4) | This
will ask to open a project. Select the project that contains the metamodel, and
hold Shift down as you press OK. If you are warned that types are
also in another project, hold down Shift as you press OK. Keeping
Shift held down avoids loading any models from those projects yet, protecting
the existing instances from being updated and hence losing that property
value. |
| 5) | Repository
| Import, and select
propertyAddedToSupertype.mxt |
You can now
look at the models back in the Graph Browser tab, opening and selecting projects
as needed, and confirm that the property slot has maintained its values in
existing instances of the subtype, and has new default values in instances of
the supertype and its other possible subtypes. If all is well, you can
commit.
