GridView has a lot of improvements over the DataGrid but it still lacks some very important features. A recurring requirement not available in the GridView is to create groups and summaries. To create summaries we can easily code the RowDataBound event. Grouping is a more complex task, and involves more coding and debugging. But when we need to combine these two features the things really start to get messy. With this in mind I have implemented the GridViewHelper, as the name suggests, a helper class to aid the creation of groups and summaries.

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Using the GridViewHelper

Below we will see some GridViewHelper samples. First we show the grid to which the groups and summaries will be created. The sample data comes from Northwind database, with a few modifications:

To create a summary for the ItemTotal column we need only the promised 2 lines of code:

First we create the GridViewHelper setting the grid in which it will act in the constructor. Then we register the summary specifying the column name and the summary operation to be performed. The result is below:

In this sample a new line was added to display the summary. Another option is to use the footer row to display the summary instead of creating a new one. When a new row is added to the grid, only the required cells to display the summarized columns are created. Using the footer, all the cells are created. In case of group summaries, generation of all cells or only the needed cells is a group attribute.

Now we will create a group. The code is shown below:

The first parameter of RegisterGroup method defines the columns to which the group must be created. It's also possible to create a composite group, consisting of an array of columns. The second parameter specifies if the group is automatic. In this case a new row will be created automatically for the group header. The third parameter specifies if the group columns must be hidden. The ApplyGroupSort method sets the sort expression of the grid as being the group columns, in this case, ShipRegion. This is required to grouping works properly, except if the data comes ordered from database.

In the above sample the column ShipRegion have been hidden:

Let's make something more interesting, let's add a summary to the created group. We need just one more line to register the summary to the group:

This time, the RegisterSummary method takes another parameter. The parameter specifies the name of the group to which the summary must be created. Group name is automatically generated from the group column names. If the group has only one column, group name will be the name of that column. If the group has more than one column, the group name will be the ordered concatenation of the columns that composes the group, joined with a plus sign ("+"): "ShipRegion+ShipName".

We can see below the grid with grouping and a summary for the group:

It's possible to create more than one group in the grid, simulating a hierarchical grouping, as seen below:

Result:

The grid after the cosmetics:

No value is displayed for the columns that don't have a summary operation defined. This makes sense because GridViewHelper doesn't know how to proceed to summarize the values found in the group rows to a unique value. This reminds the certain known message:

"Column 'column_name' is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause."

It doesn't make sense to display the columns that don't have a summary operation, and to hide them we need to call a method:

I know, it's a big big name! The resulting grid can be seen below:

Summary operations

GridViewHelper has 3 built-in summary operations: sum, average and row count. A very useful feature is the possibility of define custom summary operations. To achieve this we need to provide two methods to the GridViewHelper. A method will be called for each row found in the grid (or group) and the other will be called to retrieve the result of the summary operation. Below we have a sample of a custom summary operation. The semi-dummy operation will return the minimum value found:

In the code above we can see the required methods signatures. Both receive the summarized group and column names. If the summary is not relative to a group, the group parameter will be null. The method that is called for each row found in the grid, receives also the value of the column in the current row.

The resulting grid can be seen below :