Changes between Version 20 and Version 21 of DeveloperGuidelines/EdenMobile/Services/emDB

Timestamp:

06/12/18 08:40:56 (7 years ago)

Author:

Dominic König

Comment:

--

DeveloperGuidelines/EdenMobile/Services/emDB

@@ -201 +201 @@
 NB {{{limitby: [0,1]}}} can also be written as simply {{{limitby: 1}}}
 
-=== Aggregation and Groupby ===
-
-Aggregates can be constructed from field expressions
-
-The {{{select()}}} method accepts an object with arguments as (optional) second parameter, e.g. {{{limitby}}} and {{{orderby}}}:
-
-{{{#!js
+=== Aggregates and Groupby ===
+
+'''Aggregate expressions''' can be constructed from field expressions using operator functions, e.g.:
+
+{{{#!js
+// The total (sum) of the field 'value':
+var totalValue = table.$('value').sum();
+}}}
+
+Currently supported operators are '''count''', '''sum''', '''avg''', '''min''', and '''max'''.
+
+Aggregate expressions can be used to extract the aggregate values from rows:
+
+{{{#!js
+// The total (sum) of the field 'value':
+var totalValue = table.$('value').sum();
+...
+// Access the total in a row
+var value = row.$(totalValue);
+}}}
+
+The {{{select()}}} method of Sets accepts a groupby option:
+
+{{{#!js
+// Extract the total of values per location
+var locationID = table.$('location_id'),
+    totalValue = table.$('value').sum();
 set.select(
-    [array of fields], 
+    [locationID, totalValue], 
     {
-        limitby: [0,1], 
-        orderby: field
+        groupby: locationID, 
     },
     function(rows) {...}