Video Transcript (English)

Welcome back! Now you know how to use the compound operator with the must, filter, and mustNot clauses.

These clauses strictly include or exclude documents from our search results.

That’s very rigid. You may be wondering if there's a middle ground where we don't need to match all terms in a given search?

There is!

And in this video, we’ll walk you through the last clause in the compound operator set: the should clause.

We use the should clause when any condition in the array is enough to include the document in the results—so, conditions are optional.

We can fine-tune this behavior with the minimumShouldMatch option, which we’ll get to in a moment.

Does should stop comparing when a condition matches? Not quite. It needs to evaluate every condition so it can compute the final score.

Like the must clause, should changes the final document score by adding the individual condition scores together.

The greater the number of matching conditions, the higher the final score.

Let’s start with a familiar example.

You may recall we previously used the must clause to search for documents containing the words poet and Elizabeth in the plot field.

We’re going to use the same example but swap out the must clause for the should clause.

Let’s see what happens.

Looks like we get documents that contain the word poet, the word Elizabeth, or both.

Compare this with the results from the must clause where only documents matching both conditions are returned.

But remember when we mentioned the minimumShouldMatch option? Here’s where things get more interesting.

You can think of minimumShouldMatch as a knob that we turn to either raise or lower the number of conditions that should match. But it’s not that simple.

The allowed range of values for minimumShouldMatch differs depending on how many other clauses are present inside the compound operator.

When the only clause present is should, the minimumShouldMatch option can be set to one or greater, but not zero, and it defaults to one.

When should is not the only clause, minimumShouldMatch can be set to zero or greater. In this case, the default value is zero.

Let’s break this down a bit.

Going back to our previous example, we notice minimumShouldMatch was omitted and therefore took the default value of one.

With a minimum of one, we accept documents that satisfy any condition.

Not surprisingly, our results show documents matching the word poet or Elizabeth or both.

Notice the score increases with the number of matching conditions.

Let’s modify our previous example to include a minimumShouldMatch value of 2.

The results now include documents that meet both conditions–that is, they contain both poet and Elizabeth in the plot field.

Did you notice something interesting in the output? The results look exactly like the must clause.

When we set minimumShouldMatch to the number of conditions in the array, we have essentially created a must clause.

Note that the highest value we can set for minimumShouldMatch is the number of conditions in the should array.

So, for this example with two conditions, the maximum value of minimumShouldMatch is 2. If we set it to 3 or higher, we’ll get an error when we run the query.

Nice work! In this video, you learned how to use the compound operator with the should clause. We use the should clause when we don’t want to match all terms in a given search.

You also learned that when using the should clause, we can set the minimumShouldMatch option to determine how many conditions in our search criteria should be met.

Great work, see you in the next lesson!