Using Caché Objects - InterSystems Documentation

Objects and SQL
13.2.2.4 Reference Properties
Reference properties (that is, references to other persistent objects) are projected as fields
containing the ID portion of the OID of the referenced object. For instance, suppose a customer
object has a Rep property that refers to a SalesRep object (who is the customer' s sales representative).
If a particular customer has a sales representative with an ID of 12, then the entry
in the Rep column for that customer is also 12. Since this value matches that of the particular
row of the ID column of the referenced object, you can use this value when performing any
joins or other processing.
Note that within Caché SQL you can use a special reference syntax to easily use such references
without cumbersome JOIN syntax. For example:
SELECT Company->Name FROM Sample.Employee ORDER BY Company->Name
13.2.2.5 Embedded Object Properties
An embedded object property is projected as multiple columns in the parent class' table. One
column in the projection contains the entire object in serialized form (including all delimiters
and control characters). The rest of the columns are each for one property of the object.
The name of the column for the object property is the same as that of the object property
itself. The other column names are made up of the name of the object property, an underscore,
and the property within the embedded object. For instance, suppose a class has a Home
property containing an embedded object of type Address; Home itself has properties that
include Street and Country. The projection of the embedded object then includes the columns
named “Home_Street” and “Home_Country” . (Note that the column names are derived
from the property, Home, and not the type, Address.)
For example, the sample class Sample.Person, includes a Home property which is an
embedded object of type Sample.Address. You can use the component fields of Home via
SQL as follows:
SELECT Name, Home_City, Home_State FROM Sample.Person
WHERE Home_City %STARTSWITH 'B'
ORDER BY Home_City
Embedded objects can also include other complex forms of data:
• The projection of a reference property includes a read-only field that includes the object
reference as described in “Reference Properties” .
• The projection of an array is as a single, non-editable column that is part of the class'
table.
118 Using Caché Objects