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

From: Keean Schupke <keean@fry-it.com>
Date: Fri, 18 Mar 2011 08:45:01 +0000
Message-ID: <AANLkTikee1AnJqDjVQ=Z-j18rJfj40scD02Z-WE+HRg3@mail.gmail.com>
To: Jeremy Orlow <jorlow@chromium.org>
Cc: bugzilla@jessica.w3.org, public-webapps@w3.org
I like BDB's solution. You have one primary key you cannot mess with (say an
integer for fast comparisons) you can then add any number of secondary
indexes. With a secondary index there is a callback to generate a binary
blob that is used for indexing. The callback has access to all the fields of
the object plus any info in the closure and can use that to generate the
index data any way it likes.

This has the advantage of supporting any indexing scheme's the user may wish
to implement (by writing a custom callback), whist allowing a few common
options to be provided for the user (say a hash of all fields, or a field
name, international char set, and direction captured in a closure). The user
gets the power, the core implementation is simple, and common cases can be
implemented in an easy to use way.

var lex_order = function(field, charset, direction) {return function(object)
{/* map indexed 'field' to blob in required order */ return key;};};

Then create a new index:

object_store.validate_index(1, lex_order('name', 'us',
'ascending')).on_done(function(status) {/* status ok or error */})

validate index checks if the requested secondary index (1) exists, if it
does not it creates the index and calls the done callback (with a status
code indicating successful creation), if it does and it passes some
validation checks it also calls the done callback (with a status code
indicating successful validation). If anything goes wrong with either the
creation or validation of the secondary index if would call the done
callback with an error status code.


Cheers,
Keean.


On 18 March 2011 02:03, 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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>
Received on Friday, 18 March 2011 08:45:36 GMT

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