Example logseq queries of joining across blocks by user defined properties

logseq-join-query.md

This gist demonstrates joining across user defined block properties. To start, paste the following 3 blocks in Logseq:

- type:: person
  name:: foo
- type:: comment
  author:: foo
  text:: bar
- #+BEGIN_QUERY
  {:title "Query joining blocks by user defined properties"
   :query [:find (pull ?b2 [*])
         :where
         [?b :block/properties ?p]
         [(get ?p :type) ?type]
         [(= "person" ?type)]
         [(get ?p :name) ?name]
         [?b2 :block/properties ?p2]
         [(get ?p2 :author) ?name]]
   }
  #+END_QUERY

The third block should show the second block ?b2 as a result.

To pull a specific property from a joined block:

- #+BEGIN_QUERY
{:title "Query pulling a specific property value from a joined block"
 :query [:find ?text
       :where
       [?b :block/properties ?p]
       [(get ?p :type) ?type]
       [(= "person" ?type)]
       [(get ?p :name) ?name]
       [?b2 :block/properties ?p2]
       [(get ?p2 :author) ?name]
       [(get ?p2 :text) ?text]]
 }
#+END_QUERY

This will pull out "bar"

To make the query easier to read, we could use an input and define a rule (block-property) to make the first query:

- #+BEGIN_QUERY
{:title "Query joining user defined block properties with a rule"
 :query [:find (pull ?b2 [*])
       :in $ ?type %
       :where
       (block-property ?b :type ?type)
       (block-property ?b :name ?name)
       (block-property ?b2 :author ?name)]
  :inputs ["person"
           [[(block-property ?b ?property-name ?property-value)
            [?b :block/properties ?p]
            [(get ?p ?property-name) ?property-value]]]]
 }
#+END_QUERY