# HG changeset patch
# User František Kučera <franta-hg@frantovo.cz>
# Date 1549558505 -3600
# Node ID ce8a4be9563256d36df6ba88b144c13171321edc
# Parent  e76ca9f7d6cb983b57fbb2773fee660579ceb942
examples: Processing multiple relations with Guile

diff -r e76ca9f7d6cb -r ce8a4be95632 relpipe-data/examples-guile-aggregations.xml
--- a/relpipe-data/examples-guile-aggregations.xml	Thu Feb 07 16:24:21 2019 +0100
+++ b/relpipe-data/examples-guile-aggregations.xml	Thu Feb 07 17:55:05 2019 +0100
@@ -34,7 +34,7 @@
 Record count: 1]]></m:pre>
 
 		<p>
-			In SQL same result can be achieved by:
+			In SQL, the same result can be achieved by:
 		</p>
 
 		<m:pre jazyk="sql"><![CDATA[SELECT
diff -r e76ca9f7d6cb -r ce8a4be95632 relpipe-data/examples-guile-multiple-relations.xml
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/relpipe-data/examples-guile-multiple-relations.xml	Thu Feb 07 17:55:05 2019 +0100
@@ -0,0 +1,95 @@
+<stránka
+	xmlns="https://trac.frantovo.cz/xml-web-generator/wiki/xmlns/strana"
+	xmlns:m="https://trac.frantovo.cz/xml-web-generator/wiki/xmlns/makro">
+	
+	<nadpis>Processing multiple relations with Guile</nadpis>
+	<perex>filter some relations and others keep unaffected</perex>
+	<m:pořadí-příkladu>01800</m:pořadí-příkladu>
+
+	<text xmlns="http://www.w3.org/1999/xhtml">
+		
+		<p>
+			The <code>relpipe-tr-guile</code> is capable to process multiple relations in a single pass.
+			So we can filter some relations and let others flow unaffected through this pipeline step.
+		</p>
+
+		<m:pre jazyk="bash"><![CDATA[# define some sample relational functions:
+r1() { relpipe-in-cli generate seq 1 i integer 1 2 3; }             # seq
+r2() { relpipe-in-fstab; }                                          # fstab
+r3() { find /usr/share/sounds/ -print0 | relpipe-in-filesystem; }   # filesystem
+
+# put them together in a single stream function:
+sample-data() { r1; r2; r3; }
+
+# let them flow through our Guile transformation:
+sample-data \
+	| relpipe-tr-guile \
+		--relation fstab \
+			--where '(or (string= $type "btrfs") (string-prefix? "/mnt/" $mount_point) )' \
+		--relation filesystem \
+			--where '(and (> $size 8000) (< $size 9000) )' \
+	| relpipe-out-tabular]]></m:pre>
+	
+		<p>Such script will generate something like this:</p>
+		
+		<m:pre jazyk="text"><![CDATA[seq:
+ ╭─────────────╮
+ │ i (integer) │
+ ├─────────────┤
+ │           1 │
+ │           2 │
+ │           3 │
+ ╰─────────────╯
+Record count: 3
+
+fstab:
+ ╭─────────────────┬──────────────────────────────────────┬──────────────────────┬───────────────┬───────────────────────────────────────┬────────────────┬────────────────╮
+ │ scheme (string) │ device                      (string) │ mount_point (string) │ type (string) │ options                      (string) │ dump (integer) │ pass (integer) │
+ ├─────────────────┼──────────────────────────────────────┼──────────────────────┼───────────────┼───────────────────────────────────────┼────────────────┼────────────────┤
+ │                 │ /dev/sde                             │ /mnt/data            │ ext4          │ relatime,user_xattr,errors=remount-ro │              0 │              2 │
+ │ UUID            │ a2b5f230-a795-4f6f-a39b-9b57686c86d5 │ /home                │ btrfs         │ relatime                              │              0 │              2 │
+ │                 │ /dev/mapper/sdf_crypt                │ /mnt/private         │ xfs           │ relatime                              │              0 │              2 │
+ ╰─────────────────┴──────────────────────────────────────┴──────────────────────┴───────────────┴───────────────────────────────────────┴────────────────┴────────────────╯
+Record count: 3
+
+filesystem:
+ ╭───────────────────────────────────────────────────────────────────────────┬───────────────┬────────────────┬────────────────┬────────────────╮
+ │ path                                                             (string) │ type (string) │ size (integer) │ owner (string) │ group (string) │
+ ├───────────────────────────────────────────────────────────────────────────┼───────────────┼────────────────┼────────────────┼────────────────┤
+ │ /usr/share/sounds/Oxygen-Window-All-Desktops-Not.ogg                      │ f             │           8363 │ root           │ root           │
+ │ /usr/share/sounds/KDE-Window-All-Desktops-Not.ogg                         │ f             │           8363 │ root           │ root           │
+ │ /usr/share/sounds/Oxygen-Window-Close.ogg                                 │ f             │           8865 │ root           │ root           │
+ │ /usr/share/sounds/KDE-Window-Close.ogg                                    │ f             │           8865 │ root           │ root           │
+ │ /usr/share/sounds/KDE-Window-All-Desktops.ogg                             │ f             │           8712 │ root           │ root           │
+ │ /usr/share/sounds/Oxygen-Window-All-Desktops.ogg                          │ f             │           8712 │ root           │ root           │
+ │ /usr/share/sounds/freedesktop/stereo/power-plug.oga                       │ l             │           8748 │ root           │ root           │
+ │ /usr/share/sounds/freedesktop/stereo/bell.oga                             │ f             │           8495 │ root           │ root           │
+ │ /usr/share/sounds/freedesktop/stereo/network-connectivity-established.oga │ l             │           8748 │ root           │ root           │
+ │ /usr/share/sounds/freedesktop/stereo/device-removed.oga                   │ f             │           8500 │ root           │ root           │
+ │ /usr/share/sounds/freedesktop/stereo/device-added.oga                     │ f             │           8748 │ root           │ root           │
+ │ /usr/share/sounds/freedesktop/stereo/power-unplug.oga                     │ l             │           8500 │ root           │ root           │
+ │ /usr/share/sounds/freedesktop/stereo/network-connectivity-lost.oga        │ l             │           8500 │ root           │ root           │
+ ╰───────────────────────────────────────────────────────────────────────────┴───────────────┴────────────────┴────────────────┴────────────────╯
+Record count: 13]]></m:pre>
+
+
+		<p>
+			In Guile, we have filtered the <code>fstab</code> and <code>filesystem</code> relations
+			while the <code>seq</code> relation was kept intact.
+		</p>
+		
+		<p>
+			The <code>--relation</code> option accepts a regular expression.
+			So it is possible to process more than one relation with it (having all needed attributes in each, of course). 
+			If more <code>--relation</code> options (e.g. <code>'f.*'</code> and <code>fstab</code>) matches the same relation in the stream, only the first wins and transforms that relation.
+		</p>
+		
+		<p>
+			If we define some variables in the Guile context, they will stay there – so we can pass data across relations.
+			Thus we can do even JOIN, if we really want.
+		</p>
+
+		
+	</text>
+
+</stránka>