[Ur] Simple example using source / signal to filter a recordset using a <ctextbox> and SQL `WHERE ... LIKE` - Getting compile error `Have: xml` vs `Need: transaction` [SOLVED]

Sun Aug 16 19:33:36 EDT 2015

This compiles and runs more-or-less correctly now - using code which has
been vastly simplified compared to the previous code (in the previous
message).

The working code for the present example is in this GitHub repo:

https://github.com/StefanScott/urweb-queryX1-dyn-ctextbox-onkeyup

This message is also copied as the README on that repo.

Note: Currently, you have to add the records to the table using psql, etc.
(ie, there is no web interface to add records yet).

Actually there is also a script called `insert.sql` which will add the 50
US states for you.

The file `script.txt` contains all the Linux commands to:

- get this compiled,
- (optionally drop and) create the database, and
- (optionally) insert the 50 US states

using Postgres as the database.

---

There are a few caveats:

(1) This is basically my first attempt at FRP, so I have no idea if this is
best / proper way to wire the source and signal together.

(2) Ideally, the page should be able to display *all* the records when it
initially loads.

I tried to do this by copying the code from `<ctextbox onkeyup={...}` to
`<body onload={...}>` - but I got error messages.

(2) 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 `onclick` 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:

Question (1)

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?

Question (2)

If the answer to (1) 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 (2) *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).

---

Minor quibble:

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 see Ur/Web using FRP to
instantly filter records like this!

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