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At the end of last week's episode we created a calendar like you see here before you. This calendar can have events added to it and those events show up on the correct calendar date. But there is a problem here lurking under the hood. If we were to look at the SQL query that gets generated for this we can see that we don't have one SQL query. We in fact have 42 SQL queries, one for every date on that calendar. That's not going to cut it. Today we're going to fix that.

Let's start with the offending partial which is here in calendar views calendars day. This partial gets rendered 42 times. Since it gets rendered 42 times in this particular calendar we have a active record scope that gets called 42 times. Rather than that let's expect the data to be passed in. What I mean by that is we are currently passing in this day variable, and it's in array, it's actually a tuple. It currently has two values. The first value is the date that the day partial should render. The second value is the collection of CSS classes that should be rendered for the partial. The third one that we’re going to add now is going to be the events that we're going to render in the partial because they belong to a specific date.

We need to open up our calendar. We're going to optionally be able to pass in events now. But that presents us with a problem. We already have an optional parameter here date and we can't have two. Fortunately Ruby too gives us a way around this. We can use keyword arguments, create a keyword argument called events which defaults to an empty array and a keyword argument called date which is going to default to date.today.

Now we're going to have to persist those events that we passed in. We’ll use an instance variable and we're going to set it to the events that we passed in. Here is the tuple that contains the date and the styles, one for each of the dates that are in the array. What we're going to do here is add another value to the tuple and it's going to be a local private method called events for which takes a date.

Now let's create that private method. It’s going to be called events for. It takes a date. We're going to select over the events instance variable. We're going to then check of each these events and it occurs on date. If that date is the same as the date that was passed into the method we will return it as a new array of events.

Now the events for this particular day will be put into the tuple. The last thing that we're going to need to change here is inside of our calendar's controller we're going to need to pass the events from the active record layer into the calendar. We're going to do that by calling its keyword parameter events, and we're going to set it to just a local method. That's private called events.

I do this because I really don't like local variables strung out through my method. If I have a local variable it's very likely that it could be a local method. I’m going to extract that out. It’s a method now called events. This method is going to memorize an array of events to event.where and we're going to need to look at the occurs on date and get all of the ones where it is between date one and date two which is represented by these two question marks.

Since we pass two question marks to the SQL query we're going to need to give it two values. The first one is first calendar date, and the second one is last calendar date. If you've been following this series you may notice that we have first calendar date and last calendar date defined deep down in that calendar object. But I'm not going to pull those private local details out of the encapsulation that I had it in just so I can use it here in the controller.

It doesn't make sense to go from Rails which has active support into a Ruby class to get access to active support to come back to the Rails. We're just going to create it right here, and it looks like this. We’re going to start off with date.today. Then we're going to go to the beginning of month and the beginning of the week starting with Sunday. I'm just going to copy this method because the next method looks a lot like this method with some minor differences. We're going to go to the last calendar day and we're going to do end of month and end of week starting at Sunday.

Our work here should be complete. We should be able to restart a Rail server, then refresh the page and have a single SQL query instead of 42. Our page has reloaded and we don't notice any change in functionality at, which is good. We go to the logs and we can see that we have a lot of events and a lot of day partials being rendered, but there is only one call to the database which is right here with this events load from events where occurs on between that date and the other date.

That wraps it up for the calendar application and this series on Rubycasts. Next week we will start a new app. I hope to see you then.