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Specifying search criteria

From: Up and Running with NoSQL Databases

Video: Specifying search criteria

If you're already familiar with SQL, you might be wondering exactly how you can retrieve specific data without it. CouchDB offers querying via JavaScript. Let's navigate to the restaurant database and then select Temporary View from the View dropdown. This gives us a screen with a Map Function on the left and an optional Reduce Function on the right. For now, we're going to concentrate on the Map Function. There is also a slider here which I'm going to pull down to give us a little bit more room.

Specifying search criteria

If you're already familiar with SQL, you might be wondering exactly how you can retrieve specific data without it. CouchDB offers querying via JavaScript. Let's navigate to the restaurant database and then select Temporary View from the View dropdown. This gives us a screen with a Map Function on the left and an optional Reduce Function on the right. For now, we're going to concentrate on the Map Function. There is also a slider here which I'm going to pull down to give us a little bit more room.

The example Map Function that it gives us is one that simply calls emit. Emit takes two arguments; first the key and then the value. If we click the default function, it gives us the results; and each key is null, and every value is the complete document. Let's specify a key. Select null and then replace it with doc.name. When we click Run again, it shows the name of every document as the key and then uses the entire document as the value.

Let's specify the value. Go to the second argument and add .content. Then click Run again. Now you'll notice this view has the name as the key and the content as the value. Now let's say we wanted this view to include every document in the database except the one with the Hours property. We can wrap this emit function in an if statement. So I'm typing in if(!doc.hours) and then wrapping the emit statement in this block.

When I click Run again, it shows every document except the one with the Hours property. To get filtered data from CouchDB, use JavaScript to write a Map Function. This makes it possible to get a result set with only the data you need.

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Up and Running with NoSQL Databases

29 video lessons · 13457 viewers

Joseph LeBlanc
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