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Re: [Bug 12321] New: Add compound keys to IndexedDB

From: Jeremy Orlow <jorlow@chromium.org>
Date: Thu, 17 Mar 2011 19:03:44 -0700
Message-ID: <AANLkTim9tVBmW_m99uenTvy89CtZ9bOZbPmREy_AK9Ty@mail.gmail.com>
To: bugzilla@jessica.w3.org
Cc: public-webapps@w3.org
Here's one ugliness with A: There's no way to specify ascending
or descending for the individual components of the key.  So there's no way
for me to open a cursor that looks at one field ascending and the other
field descending.  In addition, I can't think of any easy/good ways to hack
around this.

Any thoughts on how we could address this use case?

J

On Wed, Mar 16, 2011 at 4:50 PM, <bugzilla@jessica.w3.org> wrote:

> http://www.w3.org/Bugs/Public/show_bug.cgi?id=12321
>
>           Summary: Add compound keys to IndexedDB
>           Product: WebAppsWG
>           Version: unspecified
>          Platform: PC
>        OS/Version: All
>            Status: NEW
>          Severity: normal
>          Priority: P2
>         Component: Indexed Database API
>        AssignedTo: dave.null@w3.org
>        ReportedBy: jorlow@chromium.org
>         QAContact: member-webapi-cvs@w3.org
>                CC: mike@w3.org, public-webapps@w3.org
>
>
> >From the thread "[IndexedDB] Compound and multiple keys" by Jonas Sicking,
> we're going to go with both options A and B.
>
> =========================
>
> Hi IndexedDB fans (yay!!),
>
> Problem description:
>
> One of the current shortcomings of IndexedDB is that it doesn't
> support compound indexes. I.e. indexing on more than one value. For
> example it's impossible to index on, and therefor efficiently search
> for, firstname and lastname in an objectStore which stores people. Or
> index on to-address and date sent in an objectStore holding emails.
>
> The way this is traditionally done is that multiple values are used as
> key for each individual entry in an index or objectStore. For example
> the CREATE INDEX statement in SQL can list multiple columns, and
> CREATE TABLE statment can list several columns as PRIMARY KEY.
>
> There have been a couple of suggestions how to do this in IndexedDB
>
> Option A)
> When specifying a key path in createObjectStore and createIndex, allow
> an array of key-paths to be specified. Such as
>
> store = db.createObjectStore("mystore", ["firstName", "lastName"]);
> store.add({firstName: "Benny", lastName: "Zysk", age: 28});
> store.add({firstName: "Benny", lastName: "Andersson", age: 63});
> store.add({firstName: "Charlie", lastName: "Brown", age: 8});
>
> The records are stored in the following order
> "Benny", "Andersson"
> "Benny", "Zysk"
> "Charlie", "Brown"
>
> Similarly, createIndex accepts the same syntax:
> store.createIndex("myindex", ["lastName", "age"]);
>
> Option B)
> Allowing arrays as an additional data type for keys.
> store = db.createObjectStore("mystore", "fullName");
> store.add({fullName: ["Benny", "Zysk"], age: 28});
> store.add({fullName: ["Benny", "Andersson"], age: 63});
> store.add({fullName: ["Charlie", "Brown"], age: 8});
>
> Also allows out-of-line keys using:
> store = db.createObjectStore("mystore");
> store.add({age: 28}, ["Benny", "Zysk"]);
> store.add({age: 63}, ["Benny", "Andersson"]);
> store.add({age: 8}, ["Charlie", "Brown"]);
>
> (the sort order here is the same as in option A).
>
> Similarly, if an index pointed used a keyPath which points to an
> array, this would create an entry in the index which used a compound
> key consisting of the values in the array.
>
> There are of course advantages and disadvantages with both options.
>
> Option A advantages:
> * Ensures that at objectStore/index creation time the number of keys
> are known. This allows the implementation to create and optimize the
> index using this information. This is especially useful in situations
> when the indexedDB implementation is backed by a SQL database which
> uses columns as a way to represent multiple keys.
> * Easy to use when key values appear as separate properties on the
> stored object.
> * Obvious how to sort entries.
>
> Option A disadvantages:
> * Doesn't allow compound out-of-line keys.
> * Requires multiple properties to be added to stored objects if the
> components of the key isn't available there (for example if it's
> out-of-line or stored in an array).
>
> Option B advantages:
> * Allows compound out-of-line keys.
> * Easy to use when the key values are handled as an array by other
> code. Both when using in-line and out-of-line keys.
> * Maximum flexibility since you can combine single-value keys and
> compound keys in one objectStore, as well as arrays of different
> length (we couldn't come up with use cases for this though).
>
> Option B disadvantages:
> * Requires defining sorting between single values and arrays, as well
> as between arrays of different length.
> * Requires a single property to be added to stored objects if the key
> isn't available there (for example if it's stored as separate
> properties).
>
> There is of course a third alternative: Do both Option A and Option B.
> This brings most of the advantages of both options, but also many of
> the disadvantages of both. It also adds a lot of API surface which
> could conflict with future features, so it's something I'd really like
> to avoid.
>
>
> Questions:
>
> The main question we had if there is a use case for having different
> number of compound-key-values for the entries in a index or
> objectStore? I.e. is there a case when you, in one objectStore, want
> to have one record with a compound key consisting of 2 different
> values, and another record consisting of 3, 4 or 5?
>
> In all the cases where I've used compound keys, each key-part has been
> vital. For example a table storing sale totals by quarter, country and
> price class. In this case it's obviously always going to be 3 parts to
> the compound key. Does anyone have counter examples?
>
> Similarly, are there use cases which require compound keys that
> doesn't have a hard limit on the number of values? I.e. where you
> could find out more and more detail about an item and describe that by
> adding additional values to the key.
>
> Another question is if there are databases out there which allow using
> arrays as keys, similar to option B above. It seems particularly
> likely to find "NoSQL" databases that uses this. None of the SQL
> databases we looked at allowed keying off of arrays, which isn't
> terribly surprising since SQL databases tend to create compound keys
> using separate columns, rather than multiple values in a single
> column.
>
>
> Suggested solutions:
>
> I'm currently leaning towards option A above. However I'd love to get
> input from people with more database experience than me (especially
> since mine is very SQL based), before that I don't have strong
> opinions either way.
>
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Received on Friday, 18 March 2011 02:04:38 GMT

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