This is a simple Ur/Web example which lets the user type lowercase letters [a-z]* into a <ctextbox> to instantly filter a table of 192,425 English words, using the SQL LIKE operator, displaying up to 50 rows at a time.
You can use the \copy command in psql to add the words.
The file script.txt contains all the Linux and psql commands to:
- compile the program,
- drop the database,
- create the database,
- insert the extra-long word list, and
- run the program
using Postgres as the database.
This is basically my first attempt at FRP, so I have no idea if this is best / proper way to wire the sources and signals together.
Questions
(1) Since a signal is automatically updated when its source changes (without the need to write any on_ event code), it feels kinda kludgy to be using the onkeyup event of the the <ctextbox>.
So I wonder if there is a way to update the recordset simply in response to the user typing in the <ctextbox> - without using an on_ event anywhere.
This has been done for another example - but that example used only client-side data:
https://github.com/StefanScott/urweb-ctextbox-echo
So I'm not sure if the present example, which involves reading data from the server-side (ie, running queryX1), can be done without using an on_ event - because of the questions below:
(2) For an example like this, which does a transactional "read" (but no transacational "write") on the server (ie: it uses queryX1), is it obligatory to have a "blocking" call to rpc somewhere in the code?
(3) If the answer to Question (2) is "YES", then does this further imply that a control must be used which has an on_ event (eg, currently the onkeyup event of the <ctextbox> control) - simply because it's necessary to have an on_ event somewhere, in which make the call to rpc?
I suspect the answer to (3) may "NO" here - eg, maybe the call to rpc could be done from inside a <dyn> tag, which would obviate the need for an on_ event.
I've been trying this, but so far have not gotten it to work - I keep getting type errors. (I think the result type of an on_ event is transaction unit - whereas the result type of the code in the signal attribute of a <dyn> is signal xml - so this may be causing the type errors).
Note:
The LIKE operator in Postgres is case-sensitive. There is also a non-case-sensitive version ILIKE, but it does not appear to have been implemented yet in Ur/Web.
Of course, a case-insensitive pattern-match could be done using a work-around: eg, before searching, simply convert the search string to all lower-case (resp. all upper-case), and then while doing the search, also convert the column being searched to all lower-case (resp. all upper-case).
I imagine that it might not be too difficult for a programmer to add support for Postgres ILIKE (plus whatever the corresponding operator is in MySQL) to the Ur/Web compiler.
Thanks for any feedback. It feels really cool to use Ur/Web FRP to instantly filter records like this!