I'm not sure if your taking of the problem is correct. To my mind it
runs:
You have Company and Employee. Company has many Employees and Employee
is working for one company. "Normalized" version looks like:
class Company {
@Persistent private String companyName;
@Persistent private String businessArea;
...
}
class Employee {
@Persistent private String name;
@Persistent private String address;
....
@ManyToOne
private Company company;
}
If you want to get all Employess working for a company you should
execute:
"SELECT * FROM Employee e WHERE e.company.companyName = :nameParam"
or if you want all Emloyees working for all IT companies you execute:
"SELECT * FROM Employee e WHERE e.company.businessArea = 'IT' "
...
But this query will not work in Google App Engine.
The solution is to resolve this query programmaticaly by running
several queries and filter it in memory or to "denormalize" this
scheme by moving some fields from Company to Employee
Something like:
class Epmloyee {
@Persistent String name;
@Persistent String address;
// copy of property fiels from Company
@Persistent private String companyName;
@Persistent private String businessArea;
@ManyToOne
private Company company;
}
and run
"SELECT Object(Employee) FROM Employee e WHERE e.companyName
= :nameParam"
The first solution allows keeping "normalized" version but the cost is
less effective query, the second requires to break strictly normalized
pattern but the query is much more effective (I think that it can be
10 or more times more effective). Also the second solution requires
more time while writing and updating.
But it is up to you what is more important, it is classical dilemma:
more "reads" or more "writes".
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