Difference between revisions of "FIND Examples"
| Line 1: | Line 1: | ||
==Introducing the <code>world</code> collection of countries== | ==Introducing the <code>world</code> collection of countries== | ||
| − | <p>These examples introduce NoSQL using MonogDB and PyMongo. We will be using the find() command on the collection '''world''':</p> | + | <p>These examples introduce NoSQL using MonogDB and PyMongo under Python3.4. We will be using the find() command on the collection '''world''':</p> |
<div class="hint" title="Techincal details"> | <div class="hint" title="Techincal details"> | ||
<p>The following is included in the examples but hidden</p> | <p>The following is included in the examples but hidden</p> | ||
| Line 18: | Line 18: | ||
<p class=strong>Show all the documents in world</p> | <p class=strong>Show all the documents in world</p> | ||
<pre class=def> | <pre class=def> | ||
| − | print list( | + | print(list( |
db.world.find() | db.world.find() | ||
| − | ) | + | )) |
</pre> | </pre> | ||
<div class=ans> | <div class=ans> | ||
| − | print list(db.world.find()) | + | print(list(db.world.find())) |
</div> | </div> | ||
</div> | </div> | ||
| − | <div class=q data-lang=" | + | <div class=q data-lang="py3"> |
It is also possible to just return the first document with find_one(). The Mongo shell equivalent to this is findOne() | It is also possible to just return the first document with find_one(). The Mongo shell equivalent to this is findOne() | ||
<div class="hint" title="When to use list()"> | <div class="hint" title="When to use list()"> | ||
| Line 33: | Line 33: | ||
<pre> | <pre> | ||
for document in db.<collection>.find(): | for document in db.<collection>.find(): | ||
| − | print document | + | print(document) |
</pre> | </pre> | ||
find_one() returns a single document, so a list() or loop is not needed. | find_one() returns a single document, so a list() or loop is not needed. | ||
| Line 39: | Line 39: | ||
<p class=strong>Show the first document of world</p> | <p class=strong>Show the first document of world</p> | ||
<pre class=def> | <pre class=def> | ||
| − | print db.world.find_one() | + | print(db.world.find_one()) |
</pre> | </pre> | ||
<div class=ans> | <div class=ans> | ||
| − | print db.world.find_one() | + | print(db.world.find_one()) |
</div> | </div> | ||
</div> | </div> | ||
| − | <div class=q data-lang=" | + | <div class=q data-lang="py3"> |
| − | It is also possible to skip | + | It is also possible to specify which document you want by its position. |
| + | <div class="hint" title="How to achieve the same with skip() and limit()"> | ||
| + | <pre> | ||
| + | print(list( | ||
| + | db.world.find().skip(49).limit(1) | ||
| + | )) | ||
| + | </pre> | ||
<p class=strong>Get the 50th document of world</p> | <p class=strong>Get the 50th document of world</p> | ||
<pre class=def> | <pre class=def> | ||
| − | print list( | + | print(list( |
| − | db.world.find() | + | db.world.find()[50] |
| − | ) | + | )) |
</pre> | </pre> | ||
<div class=ans> | <div class=ans> | ||
| − | print list(db.world.find() | + | print(list(db.world.find()[50])) |
</div> | </div> | ||
</div> | </div> | ||
Revision as of 12:45, 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})
)