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

- jessica

On Thu, Mar 17, 2011 at 7:03 PM, Jeremy Orlow <jorlow@chromium.org> wrote:

> 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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