iphone - Core Data: 3 table join? -

I know core data is not a database and there are many differences, is this one?

In a database, I will generally have the following

A - >> B - >> C

Many "B" in "A" C "

is the query," All I know is that c.attr = 'X' is easily written:

 from  select a, b, C where a.id = b.aid and b.id = c.bid and c.attr = 'x' in the core data, I want to do the same, but Such as using a predicate:    NSPredicate * predicate = [NSPredicate predicateWithFormat: @ "any BS.cs.atr =% @", "X"]; [Continuous Setty: Unit A ]; [Ninviidia Reagent Expression '], Reason:' Multiple keys are not allowed here '     I am right to understand whether the database is in multi-table There is a limit on joining?   I googled around and could not find a definite answer.   My current solution looks like a query:    NSPredicate * predicate = [NSPredicate predicateWi ThFormat: @ "fetch fetch for any cs.attr =% @", "X"]; ... NSArray * bs = // exec (B * b in bs) {// add ba a array} // return array    Is there any good Way? Thanks in advance for the idea.      This is going backwards   First of all, Linking ID is not required because all related objects are already connected to the relationship, meaning that construction like  like a.id = b.aid and b.id = c.bid  is not required .   Secondly, you usually set the Fetch unit for the unit getting the defined test. In this situation, if he is  c.attr = "X" , then you set your license to  C  and you should see something in your understanding:    NSPredicate * p = [NSPredicate predicateWithFormat: @ "attr =% @", xValue];    This will return an array all the  C  examples that complete the test. Then, to find any special  B  or  A , there is a case of running in respect to each  C    if your The inverse relationship is an example - >> B & lt; - >> C, then you only ask  C  for the value of  ba  such as:    AObject * anA = aCinstance.ba;    It is important to remember that you are not working with the table, you are working with the object graph. Set up to bring you a particular unit and then follow the relationships of filtered institutions.     


  
























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