Sorry, I forgot to mention that this would have to hook into the QueryParams
code as well. I don't know if it could be made type safe in the sense that
omitting the shard field in the params would throw a compile error, but at
least the selection would be uniform.
Derek
On Thu, Dec 4, 2008 at 4:41 PM, Derek Chen-Becker <[EMAIL PROTECTED]>wrote:
> OK, I see them now. I'm writing up a little section on sharding and these
> methods feel like they're not quite what I would want to use. Specifically,
> they're using different criteria for insert and retrieval, which makes it
> seem like things would get lost. In the example posting I referenced
> earlier, you use the first character of the email address for insert but
> then the primary key for retrieval. It seems like you would want to use the
> email address for retrieval as well. Is there some magic going on in the
> code that I'm missing? If not, then perhaps we need to morph this into a
> trait on the field and use a MetaMapper def that points to that field as the
> connection arbiter. Maybe something like:
>
> trait ShardSelector[T, O <: Mapper[O]] extends MappedField[T,O] {
> def selectConnection : PartialFunction[T,ConnectionIdentifier]
>
> def connection = selectConnection(this.is)
> }
>
> And in Mapper:
>
> val shardField : Can[ShardSelector] = Empty
>
> Along with some appropriate hooks into the current code.
>
> Then you could do
>
> class MyUser extends Mapper[MyUser] {
> object name extends MappedString(this) with ShardSelector {
> def selectConnection = {
> case n if n.charAt(0) < 'n' => dbAtoMConn
> case _ => dbNtoZConn
> }
> }
>
> override val shardField = Full(name)
> }
>
> Thoughts?
>
> Derek
>
>
> On Thu, Dec 4, 2008 at 4:17 PM, David Pollak <
> [EMAIL PROTECTED]> wrote:
>
>>
>>
>> On Thu, Dec 4, 2008 at 2:05 PM, Derek Chen-Becker <[EMAIL PROTECTED]>wrote:
>>
>>> OK, one last question for today before I start hacking at the text: You
>>> mention some methods here for multiple databases with a single entity:
>>
>>
>> On KeyedMetaMapper, override:
>> def dbSelectDBConnectionForFind: PartialFunction[Type,
>> ConnectionIdentifier] = Map.empty
>>
>> The ConnectionIdentifier defines which RDBMS to perform the query on.
>>
>> Also, on Mapper:
>> def dbCalculateConnectionIdentifier: PartialFunction[A,
>> ConnectionIdentifier] = Map.empty
>>
>>
>>
>>
>>>
>>>
>>> http://groups.google.com/group/liftweb/msg/76c965c189a85103?pli=1
>>>
>>> But looking in the code I can't find those methods. Are they essentially
>>> gone now? You also mentioned something better than sharding but I haven't
>>> seen anything on the list (maybe I missed it).
>>>
>>> Thanks,
>>>
>>> Derek
>>>
>>>
>>> On Thu, Dec 4, 2008 at 4:01 PM, Derek Chen-Becker <[EMAIL PROTECTED]
>>> > wrote:
>>>
>>>> Cool. I guess I'm editing my chapter this afternoon now :)
>>>>
>>>>
>>>> On Thu, Dec 4, 2008 at 3:40 PM, David Pollak <
>>>> [EMAIL PROTECTED]> wrote:
>>>>
>>>>>
>>>>>
>>>>> On Thu, Dec 4, 2008 at 7:33 AM, Derek Chen-Becker <
>>>>> [EMAIL PROTECTED]> wrote:
>>>>>
>>>>>> I'm mostly done with the rough draft of our Record/Mapper chapter and
>>>>>> I wanted to clarify a few points to make sure that my reading of the docs
>>>>>> and code is accurate:
>>>>>>
>>>>>> 1. ByRef appears to me to essentially be an old-style join (using
>>>>>> the where clause instead of join syntax). Is that accurate? Are there
>>>>>> other
>>>>>> use cases?
>>>>>>
>>>>>>
>>>>> This allows you to compare two columns in the same row. Because mapper
>>>>> does not allow for explicit joins or queries against more than one table
>>>>> at
>>>>> once (with the exception of the In construct), there's no "old style join"
>>>>> stuff.
>>>>>
>>>>> I've also changed the Join() QueryParam to PreCache... which is more
>>>>> descriptive of what it does.
>>>>>
>>>>>
>>>>>>
>>>>>> 1.
>>>>>> 2. It looks like the only way to get distinct results would be to
>>>>>> use the findAllByPreparedStatement or findAllByInsecureSql methods.
>>>>>> Is there
>>>>>> some other way to do this that I'm missing?
>>>>>>
>>>>>> Or perhaps the Distrinct() QueryParam I just added. :-)
>>>>>
>>>>>
>>>>>>
>>>>>> 1.
>>>>>> 2. The toForm method in Mapper has an overload that takes a
>>>>>> redoSnippet. What is the use case for this?
>>>>>>
>>>>>> So you can keep the current state around over the course of multiple
>>>>> form submissions when the validation fails.
>>>>>
>>>>>>
>>>>>> 1. Will it be supported in Record or has that functionality been
>>>>>> folded into something else?
>>>>>>
>>>>>> I hope it will make it into Record/Field.
>>>>>
>>>>>>
>>>>>> 1.
>>>>>> 2. It appears that the functionality of the buildSet... methods in
>>>>>> MappedField has effectievly been replaced by the setFromAny in Field.
>>>>>> Is
>>>>>> this the case, or will those buildSet functions show back up in some
>>>>>> subclass of field (it seems like there was a lot of overlap there)
>>>>>>
>>>>>> buildSet is JDBC specific and radically improves performance in
>>>>> converting a JDBC column to something that can be put into a field.
>>>>>
>>>>>>
>>>>>> 1.
>>>>>> 2. Am I reading correctly that Record no longer retains the
>>>>>> orginal value of a field when it's changed, but rather just flags the
>>>>>> field
>>>>>> as dirty? (there are no is/was methods on Field)
>>>>>>
>>>>>> Probably... but there will be is/was on Field. It's a very helpful
>>>>> construct.
>>>>>
>>>>>>
>>>>>> 1.
>>>>>>
>>>>>> These last two make sense to me since it seems like duplicated effort
>>>>>> for #4 and not much of a use case on #5 that I can think of. Any info or
>>>>>> comments would be appreciated!
>>>>>
>>>>>
>>>>> Sure... wait a few minutes for my Distinct() checkin to make it to
>>>>> GitHub
>>>>>
>>>>>
>>>>>>
>>>>>>
>>>>>> Thanks,
>>>>>>
>>>>>> Derek
>>>>>>
>>>>>>
>>>>>>
>>>>>
>>>>>
>>>>> --
>>>>> Lift, the simply functional web framework http://liftweb.net
>>>>> Collaborative Task Management http://much4.us
>>>>> Follow me: http://twitter.com/dpp
>>>>> Git some: http://github.com/dpp
>>>>>
>>>>>
>>>>>
>>>>
>>>
>>>
>>>
>>
>>
>> --
>> Lift, the simply functional web framework http://liftweb.net
>> Collaborative Task Management http://much4.us
>> Follow me: http://twitter.com/dpp
>> Git some: http://github.com/dpp
>>
>> >>
>>
>
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