Difference between revisions of "FIND Examples"
| Line 54: | Line 54: | ||
<p class=strong>Get all the data concerning france</p> | <p class=strong>Get all the data concerning france</p> | ||
<pre class=def> | <pre class=def> | ||
| − | print list(db.world.find({"name":"France"})) | + | print list( |
| + | db.world.find({"name":"France"}) | ||
| + | ) | ||
</pre> | </pre> | ||
<div class=ans> | <div class=ans> | ||
| Line 68: | Line 70: | ||
<p class=strong>Get the population of Germany</p> | <p class=strong>Get the population of Germany</p> | ||
<pre class=def> | <pre class=def> | ||
| − | print list(db.world.find({"name":"Germany"},{"population":1,"_id":0})) | + | print list( |
| + | db.world.find({"name":"Germany"},{"population":1,"_id":0}) | ||
| + | ) | ||
</pre> | </pre> | ||
<div class=ans> | <div class=ans> | ||
| Line 91: | Line 95: | ||
<p class=strong>List the countries with a population that's less than 1 million.</p> | <p class=strong>List the countries with a population that's less than 1 million.</p> | ||
<pre class=def> | <pre class=def> | ||
| − | print list(db.world.find({"population":{"$lt":1000000}},{"name":1,"_id":0})) | + | print list( |
| + | db.world.find({"population":{"$lt":1000000}},{"name":1,"_id":0}) | ||
| + | ) | ||
</pre> | </pre> | ||
<div class=ans> | <div class=ans> | ||
| Line 109: | Line 115: | ||
<p class=strong>Find the country with less than 1 million people, but over 200000km<sup>2</sup> area</p> | <p class=strong>Find the country with less than 1 million people, but over 200000km<sup>2</sup> area</p> | ||
<pre class=def> | <pre class=def> | ||
| − | print list(db.world.find({"population":{"$lt":1000000},"area":{"$gt":200000}},{"name":1,"_id":0})) | + | print list( |
| + | db.world.find({"population":{"$lt":1000000},"area":{"$gt":200000}},{"name":1,"_id":0}) | ||
| + | ) | ||
</pre> | </pre> | ||
<div class=ans> | <div class=ans> | ||
Revision as of 21:59, 14 July 2015
Introducing the world collection of countries
These examples introduce NoSQL using MonogDB and PyMongo. We will be using the find() command on the collection world:
The following is included in the examples but hidden
from pymongo import MongoClient
client = MongoClient()
client.progzoo.authenticate('scott','tiger')
db = client['progzoo']
By default, find() returns the entire contents of a collection. This is equivalent to find({})
Show all the documents in world
print list(
db.world.find()
)
print list(db.world.find())
It is also possible to just return the first document with find_one(). The Mongo shell equivalent to this is findOne()
To make things easier to understand the first document of world has been made a list of keys used in these examples.
list() is a python function and should be used with find(), as find() returns a cursor object
Show the first document of world
print db.world.find_one()
print db.world.find_one()
It is also possible to skip documents and limit the amount you return.
Get the 50th document of world
print list(
db.world.find().skip(49).limit(1)
)
print list(db.world.find().skip(49).limit(1))
Querying
By passing arguments to find() we can search for specific documents
Get all the data concerning france
print list(
db.world.find({"name":"France"})
)
print list(db.world.find({"name":"France"}))
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
print list(
db.world.find({"name":"Germany"},{"population":1,"_id":0})
)
print list(db.world.find({"name":"Germany"},{"population":1,"_id":0}))
MongoDB also allows comparisons. Syntax:
Mongo | MySQL -------------- $eq | == $gt | > $gte | >= $lt | < $lte | <= $ne | !=, <> $in | IN $nin | NOT IN
List the countries with a population that's less than 1 million.
print list(
db.world.find({"population":{"$lt":1000000}},{"name":1,"_id":0})
)
print list(db.world.find({"population":{"$lt":1000000}},{"name":1,"_id":0}))
It's also possible to have multiple conditions for an $and, $or, etc. This can be done in several ways, for example:
db.<collection>.find({<first condition>,<second condition>}
db.world.find({"population":{"$lt":1000000},"area":{"$gt":200000})
db.<collection>.find({"$and":[<first condition>,<second condition>]}
db.world.find({"$and":[{"population":{"$lt":1000000}},{"area":{"$gt":200000}}]}
Find the country with less than 1 million people, but over 200000km2 area
print list(
db.world.find({"population":{"$lt":1000000},"area":{"$gt":200000}},{"name":1,"_id":0})
)
print list(db.world.find({"population":{"$lt":1000000},"area":{"$gt":200000}},{"name":1,"_id":0}))
We can also use lists with $in and $nin:
Find the continent of Brazil, the United Kingdom, and Ghana.
print list(
db.world.find({"name":{"$in":["Brazil","United Kingdom","Ghana"]}},{"name":1,"_id":0})
)
print list(
db.world.find({"name":{"$in":["Brazil","United Kingdom","Ghana"]}},{"name":1,"_id":0})
)