Using LINQ to query nested classes in db4o?

You didn't post the exact definition of your classes but you are currently doing a cartesian product in your Linq query - you are creating every possible combination whereas you really only want "matching" combinations (since a trading day in your schema for some reason seems to be associated with a symbol). What you should do instead is a join, something like: from TradingDay t in db4o. Db join Symbol s in db4o.

Db on s. SymbolGlobal equals t. SymbolGlobal where (s.

SymbolGlobal == "IBM" && t. Date == new DateTime(2010, 10, 19)).

You didn't post the exact definition of your classes but you are currently doing a cartesian product in your Linq query - you are creating every possible combination whereas you really only want "matching" combinations (since a trading day in your schema for some reason seems to be associated with a symbol). What you should do instead is a join, something like: from TradingDay t in db4o. Db join Symbol s in db4o.

Db on s. SymbolGlobal equals t. SymbolGlobal where (s.

SymbolGlobal == "IBM" && t. Date == new DateTime(2010, 10, 19)) ...

The cause of the error is exactly right. Unfortunately, db4o doesn't really support joins that well, as it falls back to LINQ-to-objects and loads the entire database into memory in an attempt to find the correct resolution. I think it might be better to abandon LINQ and use QBE (Query By Example) to solve the problem.

– Gravitas Feb 23 at 19:44.

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