Using a string to invoke a method by its name

Tonight I was trying to create a fancy pie chart using the Gruff gem. I'm using column names as the hash key. The value is the total number of times that column was equal to true in the table.



I needed to count how many rows where that column is equal to true (select count(*) from topics where [column_name] = true). Having the column name and that total count made up a key/value pair in my hash. If a column has no occurrences of true, there's no sense in including it in my graph because it would just be 0%.

So the problem was not knowing which columns to represent in the pie graph until runtime. I could get the data from each column and use many if/else statements but I wanted a more dynamic solution. You never know when the clients want one or fifty more columns...

After some research I thought I could use Object#instance_variable_get(symbol) on an ActiveRecord object but it wasn't so. Attributes in ActiveRecord models aren't instance variables. With some help and great explanations from the OC Ruby users' group, I proceeded using Object.send(symbol) to get an attribute value by passing its name as a symbol.

In the end, I ended up not displaying the graph because the small sample didn't give much value to decision makers. Yet. Maybe I can show the top 5 favorite topics instead of this:



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My recommended books. At the bottom are my most completely read books. As you go up they become more of a reference for me.