Difference between revisions of "FIND Examples"
| Line 10: | Line 10: | ||
</div> | </div> | ||
| + | ==find and findOne== | ||
<div class=q data-lang=mongo> | <div class=q data-lang=mongo> | ||
It is also possible to just return the first document with <code>findOne()</code>. | It is also possible to just return the first document with <code>findOne()</code>. | ||
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</div> | </div> | ||
| + | ==skip and limit== | ||
<div class=q data-lang="mongo"> | <div class=q data-lang="mongo"> | ||
It is also possible to specify which document to find by its position. | It is also possible to specify which document to find by its position. | ||
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</div> | </div> | ||
| + | ==Using a projection with find== | ||
<div class=q data-lang="mongo"> | <div class=q data-lang="mongo"> | ||
By passing a second parameter to <code>find()</code> the output can be limited to certain field(s)<br/> | By passing a second parameter to <code>find()</code> the output can be limited to certain field(s)<br/> | ||
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</div> | </div> | ||
| + | ==Comparisons $eq %gt $gte $lte $ne== | ||
<div class=q data-lang="mongo"> | <div class=q data-lang="mongo"> | ||
MongoDB also allows comparisons. Syntax: | MongoDB also allows comparisons. Syntax: | ||
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</div> | </div> | ||
| + | ==Logical operations $and $or $not== | ||
<div class=q data-lang="mongo"> | <div class=q data-lang="mongo"> | ||
It's also possible to have multiple conditions for use in an $and, $or, etc. This can be done in several ways, for example: | It's also possible to have multiple conditions for use in an $and, $or, etc. This can be done in several ways, for example: | ||
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</div> | </div> | ||
| + | ==$in and $nin== | ||
<div class=q data-lang="mongo"> | <div class=q data-lang="mongo"> | ||
Lists can be used with <code>$in</code> and <code>$nin</code>: | Lists can be used with <code>$in</code> and <code>$nin</code>: | ||
| Line 122: | Line 128: | ||
</div> | </div> | ||
| + | ==Regular Expressions== | ||
<div class=q data-lang="mongo"> | <div class=q data-lang="mongo"> | ||
Pattern matching is possible with Regular Expressions (RegEx)<br /> | Pattern matching is possible with Regular Expressions (RegEx)<br /> | ||
| − | |||
| − | |||
<p class=strong>Show each country that begins with G</p> | <p class=strong>Show each country that begins with G</p> | ||
| + | [[https://docs.mongodb.com/manual/reference/operator/query/regex/]] | ||
<pre class=def> | <pre class=def> | ||
| − | db.world.find({ | + | db.world.find( |
| + | {name:{$regex:/^G/}}, | ||
| + | {name:1,continent:1,_id:0} | ||
| + | ) | ||
</pre> | </pre> | ||
<div class=ans> | <div class=ans> | ||
| − | db.world.find({ | + | db.world.find( |
| + | {name:{$regex:/^G/}}, | ||
| + | {name:1,continent:1,_id:0} | ||
| + | ) | ||
</div> | </div> | ||
</div> | </div> | ||
Revision as of 08:36, 28 October 2016
Contents
Introducing the world collection of countries
These examples introduce NoSQL using MongoDB. We will be using the find() command on the collection world:
By default, find() returns the entire contents of a collection. This is equivalent to find({})
Show all the documents in world
db.world.find()
find and findOne
It is also possible to just return the first document with findOne().
Show the first document of world
db.world.findOne()
db.world.findOne()
skip and limit
It is also possible to specify which document to find by its position.
db.world.find().skip(49).limit(1)
Get the 50th document of world
db.world.find()[49]
db.world.find()[49]
Querying
find() can filter results if a document is used as an argument.
Get all the data concerning france
db.world.findOne({"name":"France"})
db.world.findOne({"name":"France"})
Using a projection with find
By passing a second parameter to find() the output can be limited to certain field(s)
In this example 1 indicates "true" and 0 indicates "false"
A feature of MongoDB is the ObjectID or _id.
This is a unique ID MongoDB adds to each document. Unlike other keys, it has to be explicitly set to false to be excluded from the results set.
Get the population of Germany
db.world.findOne({"name":"Germany"},{"population":1,"_id":0})
Comparisons $eq %gt $gte $lte $ne
MongoDB also allows comparisons. Syntax:
Mongo | MySQL -------------- $eq | == $gt | > $gte | >= $lt | < $lte | <= $ne | !=, <> $in | IN $nin | NOT IN
List the countries with a population that's less than 1 million.
db.world.find({"population":{"$lt":1000000}},{"name":1,"_id":0})
Logical operations $and $or $not
It's also possible to have multiple conditions for use in an $and, $or, etc. This can be done in several ways, for example:
AND (implicit)
db.<collection>.find({<first condition>,<second condition>})
db.world.find({"population":{"$lt":1000000},"area":{"$gt":200000}})
AND (explicit)
db.<collection>.find({"$and":[<first condition>,<second condition>]})
db.world.find({"$and":[{"population":{"$lt":1000000}},{"area":{"$gt":200000}}]})
OR
db.<collection>.find({"$or":[<first condition>,<second condition>]})
db.world.find({"$or":[{"population":{"$lt":1000000}},{"area":{"$gt":200000}}]})
Find the countries with less than 1 million people, but over 200000km2 area
db.world.find({"population":{"$lt":1000000},"area":{"$gt":200000}},{"name":1,"_id":0})
db.world.find({"population":{"$lt":1000000},"area":{"$gt":200000}},{"name":1,"_id":0})
$in and $nin
Lists can be used with $in and $nin:
Find the continent of Brazil, the United Kingdom, and Ghana.
db.world.find(
{name:{$in:['Brazil','Ghana','United Kingdom']}},
{name:1,continent:1,_id:0}
)
db.world.find(
{name:{$in:['Brazil','Ghana','United Kingdom']}},
{name:1,continent:1,_id:0}
)Regular Expressions
Pattern matching is possible with Regular Expressions (RegEx)
Show each country that begins with G
[[1]]
db.world.find(
{name:{$regex:/^G/}},
{name:1,continent:1,_id:0}
)
db.world.find(
{name:{$regex:/^G/}},
{name:1,continent:1,_id:0}
)