Hi Steven,
Some responses inline.
Robert
On Wed, Feb 8, 2012 at 11:26, steven <jobshif...@gmail.com> wrote:
> Hi:
>
> Thank you in advance
>
> I have a question about Datastore API calls.
>
> Suppose I have a one-to-many relation ship, with two solutions as
> below:
>
> 1) solution 1
> class A
> {
> set<key> keys_for_B
> }
>
> the instance is a1 contains <b1, b2, b3>
>
> if I query for a1, and then I can get keys of b1, b2, b3; and then I
> read the b1, b2, b3.
> Does it mean there are 4 calls to datastore API calls?
If you *query* for a1, then do a bulk get on those keys you'll have:
query -> 1 scan + 1 fetch = 2 reads
bulk get -> 3 reads
So you'll have 5 reads. If you know A1's key, then you could do a get
there too which would save 1 read.
>
>
> 2) solution 2
> I build a "big-table" as
> a1, b1
> a1, b2
> a1, b3
>
> and then query as "select * from mytable where a_id = a1_id", to get 3
> rows
> I guess there is just one call, to datastore.
Generally, I would prefer the first design over introducing a third
lookup table.
Another solution here might be to include a1 as a property on your "B"
entities, possibly as an indexed list property. Then you could do one
query for Bs where a = 'a1'. This would give you 4 reads, 1 for the
scan + 3 for the entities.
>
> comparing solution 1 and 2, does it mean Google will charge me 4 times
> money for solution 1?
>
> thank you very much,
> Sincerely,
> Steven
>
>
>
>
>
>
>
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