Add a new aggregate function

August 3, 2018
aggregate-functioncode-sampledata-model

1. Problem Overview

EasyQuery supports several aggregate functions (like SUM, COUNT, AVG, etc.) out-of-the-box. However, sometimes you may need to add some other aggregate function to your model and make it appear in visual controls/widget.

2. Solution

All aggregate functions available for end-users are stored in

AggrFunctions list of DbModel class.

So, all you need to do is to add a new function to that list. Each function is an object of AggrFunction class and has the following main properties:

  • Id - a unique identifier.

  • Caption - a user-friendly name of the function which represents it in the drop-down list when the user selects the aggregate function.

  • SqlExpr - defines the way how a function is used in result SQL statement. We can use {expr} variable to specify the function’s argument

  • DisplayFormat - defines how the function is represented in columns row in ColumnsPanel control/widget. That part in double square brackets [[ … ]] is clickable - it will allow selecting another function (e.g. change it from SUM to COUNT).

3. Example

Here is an example of adding new aggregate function into model:

model.AggrFunctions.Add(new AggrFunction("MyFunc", "MyAggregate Function", "MYFUNC({expr1})", "[[My function]] of {attr1}"));