This document discusses the author's experience using MongoDB to build a web application. Some key points: - The author wanted to build a web app and renew a management tool, but found their MySQL schema had too many relations and joins. - MongoDB is schema-less and stores data as documents rather than in tables, allowing for flexible, embedded structures without defines schemas. - MongoDB has powerful querying but does not support joins or transactions between collections. For these, data would need to be denormalized and operations handled at the application level. - While MongoDB is good for high performance on single documents, the author realizes relational databases are still better for transactions and consistency across multiple documents. They want to

1. English Casual
I started to use MongoDB
2012/05/10
riywo

2. Developing Web App
❖ I wanted to build a Web App
❖ Renewal of Management Tool
❖ High performance is unnecessary
❖ Present: MySQL Schema
❖ Too many relations
❖ Fuckin’!!!

3. SELECT u.name, c.name, a.code ...
FROM users u
LEFT JOIN map USING(user_id)
LEFT JOIN classes c USING(class_id)
LEFT JOIN addresses a USING(user_id)
WHERE c.categ = ?
AND u.age >= ? AND ...

4. Schema less!!

5. Features of MongoDB
“Schema-less”
❖ MongoDB stores “documents” as BSON(binary JSON)
❖ without CREATE TABLE or ALTER TABLE
❖ TABLE => collection, RECORD => document
❖ Powerful Query
❖ next...

6. db.users.find(
{address.city:{$in:["tokyo",...]}},
{name:1}
).sort({age:-1}).limit(10).skip(5)

7. Features of MongoDB
“Schema-less”
❖ Point: “Denormalize” as much as you can
❖ not using relation or mapping table
❖ embedding to the document’s column
❖ ...Why?

8. Features of MongoDB
“no JOIN”
❖ MongoDB doesn’t support JOIN !
❖ If you want to JOIN multi collections, you should do it
on application side
❖ find document => lookup reference => find document
❖ some drivers support DBRef, but it is just format...
❖ hoge: { $ref:"coll", $id:"id" }
❖ So, intentional embedding relational documents is better

9. Features of MongoDB
“no Transaction”
❖ MongoDB doesn’t support transaction !
❖ MongoDB is designed for updating “one” document
❖ some Atomic operations($inc, findAndModify)
❖ It is difficult to update multi documents Atomically
❖ MongoDB update likes MySQL AUTOCOMMIT
’s

10. Features of MongoDB
“no Transaction”
❖ If you want to update multi documents ACID-ly...
❖ !!! You should compromise some aspects !!!
❖ Optimistic/Pessimistic Lock
❖ Two Phase Commit
❖ MVCC if possible...

11. Noooooooo!

12. I ♡ RDBMS
❖ RDBMS have great transaction function
❖ Safe for many trouble scenes
❖ But RDBMS have some weak points
❖ which are hot spots of NoSQL!
❖ So, I should learn about Database more and more
❖ I bought “Database Management Systems”
❖ Let’s read it with me!

13. Thanks