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So now before we have a look at other index types mongdb supports,

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let's see how we can configure the index types we already know

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and for that, let's again have a look at one person in our contacts data and let's create our own unique

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index.

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The ID index which you get out of the box for this field actually is unique by default

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too, this is a setting mongodb gives you

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and this ensures that you can't add another document with the same value into the same collection.

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Now sometimes you have the use case

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that you also need that behavior for a different field and therefore you can add your own unique indexes.

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Let's say for e-mail but of course we could have used login uuid if we wanted to but let's use

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that top level email element here

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and let's create an index on contacts with create index of course,

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on email let's say in ascending order and here, I now pass a second argument to create index where I

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configure this index, there

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I can now set unique to true. If I hit enter,

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I get an error that we have some duplicate keys as it seems,

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so this generally worked

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but it found a duplicate key here for Abigail Clark.

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Now let's quickly confirm this by looking into contacts and finding all contacts where the e-mail is

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this value here,

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Abigail Clark without that backslash.

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If I hit enter or I simply count that, I see I have two persons with that indeed

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and this is already one advantage of the unique index,

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we get such a warning if we want to add it or if we already had it in place and we tried to add a document

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with a value that already existed, we would have gotten an error during that insert operation.

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So unique indexes can help you as a developer

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ensure data consistency and help you avoid duplicate data for fields that you need to have unique,

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so the id, _id is unique by default but you have other use cases like maybe that email here

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too

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and the unique index is a great way for you to not just speed up your find queries but also to guarantee

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that you have unique values for that given field in that collection.