Difference between revisions of "FIND Examples"
| Line 67: | Line 67: | ||
==Querying== | ==Querying== | ||
| − | <div class=q data-lang=" | + | <div class=q data-lang="py3"> |
By passing arguments to find() we can search for specific documents | By passing arguments to find() we can search for specific documents | ||
<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( | + | print(list( |
db.world.find({"name":"France"}) | db.world.find({"name":"France"}) | ||
| − | ) | + | )) |
</pre> | </pre> | ||
<div class=ans> | <div class=ans> | ||
| − | print list(db.world.find({"name":"France"})) | + | print(list(db.world.find({"name":"France"}))) |
</div> | </div> | ||
</div> | </div> | ||
| − | <div class=q data-lang=" | + | <div class=q data-lang="py3"> |
By passing a second parameter to find() the output can be limited to certain field(s)<br/> | By passing a second parameter to find() the output can be limited to certain field(s)<br/> | ||
In this example 1 indicates "true" and 0 indicates "false"<br /><br/> | In this example 1 indicates "true" and 0 indicates "false"<br /><br/> | ||
| Line 87: | Line 87: | ||
<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( | + | print(list( |
db.world.find({"name":"Germany"},{"population":1,"_id":0}) | db.world.find({"name":"Germany"},{"population":1,"_id":0}) | ||
| − | ) | + | )) |
</pre> | </pre> | ||
<div class=ans> | <div class=ans> | ||
| − | print list(db.world.find({"name":"Germany"},{"population":1,"_id":0})) | + | print(list(db.world.find({"name":"Germany"},{"population":1,"_id":0}))) |
</div> | </div> | ||
</div> | </div> | ||
| − | <div class=q data-lang=" | + | <div class=q data-lang="py3"> |
MongoDB also allows comparisons. Syntax: | MongoDB also allows comparisons. Syntax: | ||
<pre> | <pre> | ||
| Line 112: | Line 112: | ||
<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( | + | print(list( |
db.world.find({"population":{"$lt":1000000}},{"name":1,"_id":0}) | db.world.find({"population":{"$lt":1000000}},{"name":1,"_id":0}) | ||
| − | ) | + | )) |
</pre> | </pre> | ||
<div class=ans> | <div class=ans> | ||
| − | print list(db.world.find({"population":{"$lt":1000000}},{"name":1,"_id":0})) | + | print(list(db.world.find({"population":{"$lt":1000000}},{"name":1,"_id":0}))) |
</div> | </div> | ||
</div> | </div> | ||
| Line 132: | Line 132: | ||
<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( | + | print(list( |
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}) | ||
| − | ) | + | )) |
</pre> | </pre> | ||
<div class=ans> | <div class=ans> | ||
| − | 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}))) |
</div> | </div> | ||
</div> | </div> | ||
| − | <div class=q data-lang=" | + | <div class=q data-lang="py3"> |
We can also use lists with $in and $nin: | We can also use lists with $in and $nin: | ||
<p class=strong>Find the continent of Brazil, the United Kingdom, and Ghana.</p> | <p class=strong>Find the continent of Brazil, the United Kingdom, and Ghana.</p> | ||
<pre class=def> | <pre class=def> | ||
| − | print list( | + | print(list( |
db.world.find({"name":{"$in":["Brazil","United Kingdom","Ghana"]}},{"name":1,"_id":0}) | db.world.find({"name":{"$in":["Brazil","United Kingdom","Ghana"]}},{"name":1,"_id":0}) | ||
| − | ) | + | )) |
</pre> | </pre> | ||
<div class=ans> | <div class=ans> | ||
| − | print list( | + | print(list(db.world.find({"name":{"$in":["Brazil","United Kingdom","Ghana"]}},{"name":1,"_id":0}))) |
| − | |||
| − | ) | ||
</div> | </div> | ||
</div> | </div> | ||
Revision as of 12:49, 15 July 2015
Introducing the world collection of countries
These examples introduce NoSQL using MonogDB and PyMongo under Python3.4. We will be using the find() command on the collection world:
The following is included in the examples but hidden
import io
import sys
sys.stdout = io.TextIOWrapper(sys.stdout.buffer, encoding='utf-16')
#MONGO
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()
list() is a python function and is a convient way to display a cursor object. Alternatively you could use a for loop:
for document in db.<collection>.find():
print(document)
find_one() returns a single document, so a list() or loop is not needed.
Show the first document of world
print(db.world.find_one())
print(db.world.find_one())
It is also possible to specify which document you want by its position.
print(list(
db.world.find().skip(49).limit(1)
))
Get the 50th document of world
print(list(
db.world.find()[50]
))
print(list(db.world.find()[50]))
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})))