Mapping an object using values from multiple tables

Question

Is it possible to use values looked up in other tables when mapping an object?
For example: I have three tables. In table 1, I have fields for 'cityCode' and 'stateCode'. Table 2 is a state table which contains a list of stateCodes and corresponding stateIds. Table 3 is a city table with cityCodes listed by stateId (the city code is unique within the stateId but can be duplicated under other stateIds). Table 3 also contains the cityName for the matching cityCode/stateId pair.
I am ultimately trying to match a cityName to a cityCode. I can't figure out how to tell toplink use the stateId returned when mapping Table 1 to Table 2 via stateCode when mapping cityCode in Table 1 to Table 3.
Any help is greatly appreciated
--matt                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               

Answer 1

What does your object model look like, do you have a single object with data from all three tables in it?
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In general because the cardinality of the tables and usage does not match, I would not recommend using multiple tables to map this. Instead define a CityNameManager class that preloads and stores all of the city names for each state, (possible lazy initializing each set of cities per state). Your getCityName() method in your class would then just use this manager.
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You could map the multiple tables but it may be difficult, and would most likely need to be read-only because I don't think you want to insert into the table2 or 3. You basically have a foreign key table1.stateCode => table2.stateCode, (table1.cityCode, table2.stateId) => (table3.cityCode, table3.stateId). You probably cannot define this in the Mapping Workbench, so would need to use the ClassDescriptor code API and an amendment method. If you can't get the foreign keys to work you can always use the descriptor multipleTableJoinExpression and define the join directly.
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You could also define a OneToOneMapping to the CityName from your object using the cityCode and using a selectionCriteria() on your mapping to provide an expression that uses the getTable() method to join to the intermediate table.
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<p>James Sutherland