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Re: [Makumba-user] new mak:listGroup feature
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From: Cristian B. <cr...@cs...> - 2012-11-07 09:41:05
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Hi Rudi, great to hear from you! On 2012-11-07 09.28, Rudolf Mayer wrote: > Nice work! but I wonder, isn't that similar to what the > hasValueChanged() function would do? indeed but this is done in a UI-hierarchical way. Basically in the HTML/JSP/source tree you want the "grouping" element (customer) to be the "father" of the "grouped" element (sales data). I am not sure "group" is the best terminology here but that's another story I was thinking strategically in e.g. a graphical environment which does not necessarily produce HTML (consider the Swing thing I have done and recently published). There you can't affect the structure/hierarchy by way of c:if, and even if you could, it is good for the user to see the hierarchy directly in the "source". With hasValueChanged() this doesn't happen. best, cristi > On 6 November 2012 01:42, Cristian Bogdan <cr...@na...> wrote: >> Dear makumba users, >> >> I've implemented <mak:list distinct="true"> the other day as I needed it >> in a personal project. >> >> Say I have a Sales table that has a (string) field customer. I want to >> list the data in the table but I want to sort by customer and format the >> output nicely for each customer. There is no customer table (or there >> may be, but the customer name is repeated in the Sales table for query >> optimization reasons, i.e. the data is not in "normal form", which often >> brings the need for using distinct) >> >> Using distinct=true >> >> <mak:list from="Sales c" distinct="true"> >> nice formatting <mak:value expr="c.customer" /> more formatting >> <mak:list from="Sales data" where ="data.customer=c.customer">...show >> data...</mak:list> >> </mak:list> >> >> This is a performance disaster because >> - the table is joined unnecessarily with itself, for a large table this is >> unacceptable >> - the SELECT DISTINCT is slower because it needs to examine all results >> and eliminate duplicates >> >> The other option is to do a single mak:list ordered by customer, and to >> use c:if to detect when the customer value changed from the previous >> mak:list iteration, and display the nice formatting then. This is much >> faster (no join, no DISTINCT) but the code is ugly. Besides, there are >> really two lists (one with customers, one with sales per customer) which >> are not visible in the code as nicely embedded tags, as they are in the >> distinct version above. >> >> It is important that the code/tag hierarchy respects the user interface >> hierarchy, and this is often provided by makumba. >> >> So I implemented this approach >> >> <mak:list from="Sales data" orderby="data.customer"> >> nice formatting <mak:value expr="data.customer" /> more formatting >> <mak:listGroup>...show data...</mak:listGroup> >> </mak:list> >> >> Basically the listGroup will hide everything _outside_ it (and inside the >> mak:list) unless one of the mak:values outside it (and inside the >> mak:list) changes value from the previous mak:list iteration. Currently >> this hiding is implemented via a HTML comment :). More sophisticated >> implementation can be thought of (a special page writer that can be turned >> on and off), but this version is anyway thousands of times faster than >> the DISTINCT version. >> >> Some more features: >> - it is possible to have a mak:list in a listGroup, >> - the mak:list in a listGroup can contain listGroup in its turn >> - listGroup can declare a separator >> - a listGroup in a listGroup would make sense but it doesn't work yet >> >> As you can see, listGroup brings a list-like notation even if there is no >> separate table (two embedded iterations over the same table). There are >> more cases when the data that you want to list does not come from a table: >> sequences of numbers, date intervals, etc. Such small "data sources" could >> be easily integrated and "joined" with DB data >> >> all the best, >> >> cristi >> >> >> >> >> >> >> ------------------------------------------------------------------------------ >> LogMeIn Central: Instant, anywhere, Remote PC access and management. >> Stay in control, update software, and manage PCs from one command center >> Diagnose problems and improve visibility into emerging IT issues >> Automate, monitor and manage. Do more in less time with Central >> http://p.sf.net/sfu/logmein12331_d2d >> _______________________________________________ >> Makumba-user mailing list >> Mak...@li... >> https://lists.sourceforge.net/lists/listinfo/makumba-user >> |