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In the last section we started writing a query that would not only find but also update the appropriate

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survey in one entire ago.

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So we essentially will end up just running this operation right here.

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The correct surveys should be found and then correctly updated based on the criteria that we're going

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to pass in this second object right here.

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And so that's where we kind of left things off.

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We need to figure out exactly how we are going to update the appropriate survey like this one that we

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find right here.

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Now when the previous code that we were just looking at at the previous kind of iteration of this query

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that I was saying was really bad.

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You'll notice that there was essentially two big things that we wanted to do over here.

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The first thing we wanted to do was make sure that we updated the appropriate recipients responded propertied

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true.

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And then we wanted to increment the number of answers or the number of responses either the yes property

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or the no property by exactly one.

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And then we also set the last responded property as well.

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So right now let's just kind of forget this last responded property for just a minute because we didn't

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really care.

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You know this isn't the most critical property in the world.

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This was just a property that gave a little bit of information to our users to tell them hey here's

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the last time someone voted on a particular survey.

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So I want to just focus on these two properties right here.

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I just want to update the number of responses and I want to update the given recipient to have responded

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property of true.

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So back over at our query that we're in the process of writing I'm going to find the second object right

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here and inside of here we're going to place the logic that is going to update the respondent property

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on the recipient and to give an answer or then the given choice of yes or no.

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So let's take care of that choice property first.

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All right.

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Now this is going to be a little bit crazy.

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We're going to write out the code for it and we'll talk about exactly what it's doing.

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So inside of this second object I'm going to write dollar sign.

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I can see that's going to be an object that has brackets square brackets mind you choice Colan one like

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so.

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So triple check your typing make sure you've got exactly the same code right here.

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Now before we talk about what's going on I want to write up at the top remember that our choice property

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is always going to be either yes or no.

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So just remind our going to places up here just remind you what the choice property is going to be.

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All right.

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So let's talk about what is going on right here.

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This dollar sign I see thing is called a mongo operator.

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It allows us to put together some kind of intelligent or slightly intelligent logic inside of a query

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that we issue to our database.

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So this says find the choice property and remember remember choice is going to be either yes or no.

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We'll talk about what these spring spare rocket or square brackets excuse me I mean in just a second.

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So essentially find either the property or the no property and increment so I can see stands for increment

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it by exactly 1.

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So in other words provide one vote to either the yes or the no property on the given survey that was

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just found.

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Now of course we want to allow the decision of whether or not we are incrementing the yes or the no

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property to be determined on the fly.

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So in order to kind of calculate the key to use inside this object right here we're going to use a little

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bit of yes 20:16 syntax called qi interpellation.

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So if we put on here square brackets choice like so this does not create an array.

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Let me be really clear about that.

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It does not create an array.

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Instead when this object right here is the value evaluated by the javascript runtime it's going to say

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OK what's the value of the choice variable.

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If the value of choice is yes then it's going to replace this thing right here with yes.

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Otherwise if it's no it's going to replace it with no.

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So in other words we are saying we don't really know at the time that we are writing the code whether

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choice is going to be yes or no.

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So only when we are kind of trying to actually update the given survey only after we have an actual

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choice assigned will we actually figure out what this key right or should be in total.

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Again this little block right here says increment either yes or no by exactly 1 on the survey record

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that was found.

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OK.

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So that clearly takes care of step 1.

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We are incrementing the appropriate feedback property by one.

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Now the next thing we have to do is a little bit more complicated.

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Believe it or not the next thing we have to do is make sure that we take the recipient who has found

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and we update their responded property to True.

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So on this one we're just going to write out the code for applying this update and we'll talk about

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exactly what's going on.

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So after this dollar sign Inc.

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And this object direct here we'll put a comma and then the next line down.

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So this is another key value property inside the second object right here.

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We're going to say Dollar Sign set we're going to pass in an object.

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And this is where things get weird.

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We're you give it a key inside of a string of recipients dot dollars dollar sign dot responded are going

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to say that's going to be true like so.

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OK.

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So I think that in your head you understand more or less what this line is meant to accomplish.

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It is meant to update this responded property to True.

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But the real question is how does this kind of modifier actually work how does this actually update

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that property.

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So we're doing here is we are making use of another Mongo operator.

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We are saying that we want to set or update one of the properties inside of the survey record that was

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found by this initial query right here.

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So we are saying in the survey that was found look at the recipient's sub document collection inside

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that Subotnick collection.

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There are a bunch of different records to make sure that we are updating just the recipient that we

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really care about.

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We place dollar sign right here this dollar sign lines up with the dollar element or Elham match from

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the original query that was issued up here.

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So remember this line right here is going to find just the sub document collection recipient that we

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actually care about.

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And so maybe they are at index 500 inside of our list of recipients.

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So that 500 of an index is then used right here in place of the dollar sign.

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So you can imagine this thing is saying go into some documents collection find the appropriate recipient

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who was just found in the original query right here.

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Look at the respondent property and set that property to now be true rather than false like it was before.

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And that's pretty much it.

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So I know this clearly has we've written it out is really confusing.

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It's really crazy.

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But I want to give you a very intense a really in-depth query that you might find yourself writing when

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you are making use of Mongo.

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So let's walk through the entire thing again.

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We are saying look at the survey Compare can find an update exactly one record inside that collection

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we want to find the survey with this given ID who has a recipient with a given email and has not yet

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responded to the survey.

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After this one singular survey has been found make this following update to it increment the choice

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either yes or no by one and update the recipient who we just found in the original query update the

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respondent property to True because they have now actually responded so it's no longer responding false.

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It is now responded true.

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So that's very much the query interval.

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So this syntax right here.

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Yeah it's kind of nasty and you're probably sitting there thinking how in the world would I ever figure

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out how to write this query myself.

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And you know it's just something that comes with a little bit of experience.

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Again I'll give you at least a little bit of a toolset or just a very quick couple of tips on exactly

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how you can approach queries like this and figure out how to write them yourself.

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But the end of the day what I want you to really focus on is the fact that when we issue this query

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right here the entire thing from find the correct survey and then updating the survey is executed entirely

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inside of our Mongo database.

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So we are never going to exchange any information whatsoever from our express server back over to Mago

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DB.

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There's no communication there of the actual data.

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We are just sending one instruction over to Mongo and saying hey make this update happen like just do

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the thing Mungo's going to process this update and that's it.

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We never have to go through the very laborious process of fetching the record pulling over the whole

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as the recipients searching through them.

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Updating one recipient and then saving back the entire record which in reality is a very long running

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process.

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OK so I think that we probably railed on about this query long enough.

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I think that you probably understand a couple of the considerations around it.

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So at this point let's take a quick break.

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We're going to continue in the next section and when we do we're going to move this query that we just

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wrote right here back into our survey routes J.S. file and so we will make sure that for every event

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in our events array we attempt to actually run and apply this query right here.

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So quick break and I'll see you in just a minute.