- From: Jeremy Orlow <jorlow@chromium.org>
- Date: Thu, 20 Jan 2011 10:33:35 +0000
- To: Keean Schupke <keean@fry-it.com>
- Cc: Jonas Sicking <jonas@sicking.cc>, Webapps WG <public-webapps@w3.org>
- Message-ID: <AANLkTinweMQFhXzwjOzwNBi3HfgYskgKqqgvsG+jMfKY@mail.gmail.com>
Ok. So what's the resolution? Let's bug it! On Fri, Dec 10, 2010 at 12:34 PM, Jeremy Orlow <jorlow@chromium.org> wrote: > Any other thoughts on this issue? > > > On Thu, Dec 2, 2010 at 7:19 AM, Keean Schupke <keean@fry-it.com> wrote: > >> I think I prefer A. Declaring the keys in advance is stating to sound a >> little like a schema, and when you go down that route you end up at SQL >> schemas (which is a good thing in my opinion). I understand however that >> some people are not so comfortable with the idea of a schema, and these >> people seem to be the kind of people that like IndexedDB. So, although I >> prefer A for me, I would have to say B for IndexedDB. >> >> So in conclusion: I think "B" is the better choice for IndexedDB, as it is >> more consistent with the design of IDB. >> >> As for the cons of "B", sorting an array is just like sorting a string, >> and it already supports string types. >> >> Surely there is also option "C": >> >> store.add({firstName: "Benny", lastName: "Zysk", age: 28}, ["firstName", >> "lastName"]); >> store.add({firstName: "Benny", lastName: "Andersson", age: >> 63}, ["firstName", "lastName"]); >> >> Like "A", but listing the properties to include in the composite index >> with each add, therefore avoiding the "schema"... >> >> >> As for layering the Relational API over the top, It doesn't make any >> difference, but I would prefer whichever has the best performance. >> >> >> Cheers, >> Keean. >> >> >> On 2 December 2010 00:57, Jonas Sicking <jonas@sicking.cc> wrote: >> >>> 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. >>> >>> / Jonas >>> >>> >> >
Received on Thursday, 20 January 2011 10:52:56 UTC