On Nov 4, 10:20 pm, Eli <[email protected]> wrote:
> I want to get our wordology clear (let me know where I am going
> wrong):
>
> A Model in AppEngine is equivalent to a Table in SQL (or, if you like,
> it is equivalent to the Table Schema).
>
> An Entity in a Model is equivalent to a Row in a Table. (so.. a Model
> is potentially a collection of Entities in the same way a Table is
> potentially a collection of Rows)
>
> Properties (of the Entities) in a Model are equivalent to Columns (of
> the Rows) in a Table.
>
> Maybe the confusion comes in with the wordage: "all of the index rows
> for that entity must be updated"
>
> What is an index row? I am assuming that an "index row" for a certain
> property is a row entry in BigTable that contains all index
> information for all Entities in the given Model that have that
> property defined.
No, there is an single index row for each property of each entity.
> So, there would be an "index row" for the Month Property of your Stats
> Model defined above.
Yes.
> And, when an Entity was inserted or Deleted for
> this Stats Model, the index row for Month would have to be rebuilt.
No. The index rows are like the entity rows. Only the rows in the
index which correspond to the properties for that particular entity
need to be inserted/deleted.
> I understand that I can be completely wrong on this.. but let me know
> where the flaw in my understanding of Entities, Models and Indexes
> might be.
I like to think of it something like this:
create table BigTable (
key varchar primary key,
properties blob
);
All the properties are serialised (using Protocol Buffers) into the
blob. This is how you can have entities of the same type with
different properties.
When you put() an entity, the db looks at the properties blob (because
it understands the serialisation format) and if it finds eg. a single
integer property, it inserts a row into the AscendingIndexBigTable,
and another into the DescendingIndexBigTable.
The indexes could look similar to the entity table, except imagine
changing the key key to "eli/E1/a1=42" for the a1 property.
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