API/Queries/Attributes.md

@@ -13,7 +13,7 @@ The IronAPI supports these options:
 - [order_by](#ordering)
 - [group_by](#group-by)
 - [collapse](#collapse)
-- having
+- [having](#having)
 
 
 This document will cover some of the options with specific examples.
@@ -447,6 +447,10 @@ A list of how many users have which value in the json attribute  `settings->>'en
 When "collape" is set to a true value, indicates that any rows fetched from joined has_many relationships
 are to be aggregated into the corresponding "parent" object:
 
+Note that "prefetch" is a shortcut for "join", adding all columns from the joined related sources as "+columns" and setting "collapse" to a true value.
+
+https://metacpan.org/pod/distribution/DBIx-Class/lib/DBIx/Class/ResultSet.pm#collapse
+
 ## Restrictions
 
 The only valid values are `0` and `1`.
@@ -529,9 +533,46 @@ Without "collapse", there would be an entry for each module+entity combination:
 
 ````
 
-Note that "prefetch" is a shortcut for "join", adding all columns from the joined related sources as "+columns" and setting "collapse" to a true value.
+# Having
+
+`having` specifies a search condition for a group or an aggregate.
+
+For filtering with a function, this format is supported: `{'count(id)' => {"!=", 1}}`. It will be translated to
+SQL `\[ 'count(id) != ?', 100 ]`. Only (permitted functions)[#permitted-functions] may be called.
+
+https://metacpan.org/pod/DBIx::Class::ResultSet#having
+
+## Restrictions
+
+Only (permitted functions)[#permitted-functions] may be called. As operators, `!=`. `=`, `<` , `<=`, `>` and `>=` are currently supported.
+The value for the comparison must be integer.
+
+## Examples
+
+List only those modules which have entites attached:
+
+`POST /data/system/module/query`
+
+```json
+{
+  "attrs": {
+    "join": "system__entity__module",
+    "columns": "me.name",
+    "+select": [
+      {
+        "count": "system__entity__module.id",
+        "-as" : "entity_count"
+      }
+    ],
+    "+as": [
+      "entity_count"
+    ],
+    "group_by": "me.name",
+    "having" : {"count(system__entity__module.id)" : {">" : 0}}
+  }
+}
+```
 
-https://metacpan.org/pod/distribution/DBIx-Class/lib/DBIx/Class/ResultSet.pm#collapse
 
 # Permitted Column Names