Limitations
There are the following limitations in the current release of the
Relational DAS:
-
No support for nulls. There is no support for SQL NULL type.
It is not legal to assign PHP NULL to a data object property
and the Relational DAS will not write that back as a NULL to the
database. If nulls are found in the database on a query,
the property will remain unset.
-
Only two types of SDO relationship. The metadata described below
allows the Relational DAS to model just two types of SDO relationship:
multi-valued containment relationships and single-valued
non-containment references. In SDO, whether a property describes a
single- or multi-valued relationship, and whether it is containment
or non-containment, are independent. The full range of possibilities
that SDO allows cannot all be defined. There may be relationships
that it would be useful to model but which the current implementation
cannot manage.
One example is a single-valued containment relationship.
-
No support for the full range of SDO data types. The Relational
DAS defines all primitive properties in the SDO model as being
of type string. SDO defines a richer set of types containing various
integer, float, boolean and data and time types. String is adequate
for the purposes of the Relational DAS since the combination of PHP,
PDO and the database will ensure that values passed as strings
will be converted to the proper type before being put in the database.
This does affect some scenarios in which the Relational DAS has
to work with a data graph that has come from or will go to a
different DAS.
-
Only one foreign key per table.
The metadata only provides the means to specify one foreign key
per table. This foreign key may be mapped to one of the two types of
SDO relationship supported. Obviously there are some scenarios
that cannot be described under this limitation - it is not possible
to have two non-containment references from one table to another
for example.
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