Schema Design
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This document summarizes a presentation on schema design in MongoDB. Some key points covered include: - MongoDB uses collections instead of tables and documents instead of rows. - Schema design focuses on how an application will access and use data, rather than on data storage. - Embedded documents are useful for one-to-one relationships but can impact write performance. - Linked data using references is more flexible and ensures data integrity. - Examples demonstrate different approaches to modeling one-to-one, one-to-many relationships and categories.
![What is a Document?
{
_id:
“123”,
title:
"MongoDB:
The
Definitive
Guide",
authors:
[
{
_id:
"kchodorow",
name:
"Kristina
Chodorow“
},
{
_id:
"mdirold",
name:
“Mike
Dirolf“
}
],
published_date:
ISODate("2010-‐09-‐24"),
pages:
216,
language:
"English",
publisher:
{
name:
"O’Reilly
Media",
founded:
"1980",
location:
"CA"
}
}](https://image.slidesharecdn.com/schema-20design-131122142938-phpapp02/85/Schema-Design-6-320.jpg)
![A Patron and their Addresses
> patron = db.patrons.find({ _id : “bob” })
{
_id: “bob",
name: “Bob Knowitall",
addresses: [
{street: "1 Vernon St.", city: "Newton", …},
{street: "52 Main St.", city: "Boston", …},
]
}](https://image.slidesharecdn.com/schema-20design-131122142938-phpapp02/85/Schema-Design-18-320.jpg)
![A Patron and their Addresses
> patron = db.patrons.find({ _id : “bob” })
{
_id: “bob",
name: “Bob Knowitall",
addresses: [
{street: "1 Vernon St.", city: "Newton", …},
{street: "52 Main St.", city: "Boston", …},
]
}
> patron = db.patrons.find({ _id : “joe” })
{
_id: "joe",
name: "Joe Bookreader",
address: { street: "123 Fake St. ", city: "Faketon", …}
}](https://image.slidesharecdn.com/schema-20design-131122142938-phpapp02/85/Schema-Design-19-320.jpg)
![Book with embedded Publisher
> book = db.books.find({ _id : “123” })
{
_id: “123”,
title: "MongoDB: The Definitive Guide",
authors: [ "Kristina Chodorow", "Mike Dirolf" ],
published_date: ISODate("2010-09-24"),
pages: 216,
language: "English",
publisher: {
name: "O’Reilly Media",
founded: "1980",
location: "CA"
}
}](https://image.slidesharecdn.com/schema-20design-131122142938-phpapp02/85/Schema-Design-23-320.jpg)
![Book with linked Publisher
> book = db.books.find({ _id: “123” })
{
_id: “123”,
publisher_id: “oreilly”,
title: "MongoDB: The Definitive Guide",
authors: [ "Kristina Chodorow", "Mike Dirolf" ],
published_date: ISODate("2010-09-24"),
pages: 216,
language: "English"
}
> db.publishers.find({ _id : book.publisher_id })
{
_id: “oreilly”,
name: "O’Reilly Media",
founded: "1980",
location: "CA"
}](https://image.slidesharecdn.com/schema-20design-131122142938-phpapp02/85/Schema-Design-27-320.jpg)
![Publisher with linked Books
> publisher = db.publishers.find({ _id : “oreilly” })
{
_id: “oreilly”,
name: "O’Reilly Media",
founded: "1980",
location: "CA“,
books: [“123”,…]
}
> books = db.books.find({ _id: { $in : publisher.books } })](https://image.slidesharecdn.com/schema-20design-131122142938-phpapp02/85/Schema-Design-29-320.jpg)
![Books with linked Authors
> book = db.books.find({ _id : “123” })
{
_id: “123”,
title: "MongoDB: The Definitive Guide",
published_date: ISODate("2010-09-24"),
pages: 216,
language: "English“,
authors: [“kchodorow”, “mdirolf”]
}
> authors = db.authors.find({ _id : { $in : book.authors } })
{ _id: "kchodorow", name: "Kristina Chodorow”, hometown: … }
{ _id: “mdirolf", name: “Mike Dirolf“, hometown: … }](https://image.slidesharecdn.com/schema-20design-131122142938-phpapp02/85/Schema-Design-31-320.jpg)
![Books with linked Authors
> book = db.books.find({ _id : “123” })
{
_id: “123”,
title: "MongoDB: The Definitive Guide",
published_date: ISODate("2010-09-24"),
pages: 216,
language: "English“,
authors = [
{ id: "kchodorow", name: "Kristina Chodorow” },
{ id: "mdirolf", name: "Mike Dirolf” }
]
}](https://image.slidesharecdn.com/schema-20design-131122142938-phpapp02/85/Schema-Design-32-320.jpg)
![Authors with linked Books
> authors = db.authors.find({ _id : “kchodorow” })
{
_id: "kchodorow",
name: "Kristina Chodorow",
hometown: "Cincinnati",
books: [ {id: “123”, title : "MongoDB: The Definitive Guide“ } ]
}](https://image.slidesharecdn.com/schema-20design-131122142938-phpapp02/85/Schema-Design-34-320.jpg)
![Links on both Authors and Books
> authors = db.authors.find({ _id : “kchodorow” })
{
_id: "kchodorow",
name: "Kristina Chodorow",
hometown: "Cincinnati",
books: [ {id: “123”, title : "MongoDB: The Definitive Guide“ } ]
}
> book = db.books.find({ _id : “123” })
{
_id: “123”,
title: "MongoDB: The Definitive Guide",
authors = [
{ id: "kchodorow", name: "Kristina Chodorow” },
{ id: "mdirolf", name: "Mike Dirolf” }
]
}](https://image.slidesharecdn.com/schema-20design-131122142938-phpapp02/85/Schema-Design-35-320.jpg)
![Categories as an Array
> book = db.books.find({ _id : “123” })
{
_id: “123”,
title: "MongoDB: The Definitive Guide",
categories: [“MongoDB”, “Databases”, “Programming”]
}
> db.books.find({ categories: “Databases” })](https://image.slidesharecdn.com/schema-20design-131122142938-phpapp02/85/Schema-Design-39-320.jpg)
Schema Design
- 1. #MongoDBDays Schema Design Craig Wilson Software Engineer, MongoDB @craiggwilson
- 2. All application development is Schema Design
- 3. Success comes from a Proper Data Structure
- 4. Terminology RDBMS MongoDB Database ➜ Database Table ➜ Collection Row ➜ Document Index ➜ Index Join ➜ Embedding & Linking
- 6. What is a Document? { _id: “123”, title: "MongoDB: The Definitive Guide", authors: [ { _id: "kchodorow", name: "Kristina Chodorow“ }, { _id: "mdirold", name: “Mike Dirolf“ } ], published_date: ISODate("2010-‐09-‐24"), pages: 216, language: "English", publisher: { name: "O’Reilly Media", founded: "1980", location: "CA" } }
- 7. Traditional Schema Design Focus on Data Storage
- 8. Document Schema Design Focus on Data Usage
- 9. Traditional Schema Design What answers do I have?
- 10. Document Schema Design What questions do I have?
- 11. Schema Design By Example
- 12. Library Management Application • Patrons/Users • Books • Authors • Publishers
- 13. Question: What is a Patron’s Address?
- 14. A Patron and their Address > patron = db.patrons.find({ _id : “joe” }) { _id: "joe“, name: "Joe Bookreader” } > address = db.addresses.find({ _id : “joe” }) { _id: "joe“, street: "123 Fake St. ", city: "Faketon", state: "MA", zip: 12345 }
- 15. A Patron and their Address > patron = db.patrons.find({ _id : “joe” }) { _id: "joe", name: "Joe Bookreader", address: { street: "123 Fake St. ", city: "Faketon", state: "MA", zip: 12345 } }
- 16. One-to-One Relationships • “Belongs to” relationships are often embedded. • Holistic representation of entities with their embedded attributes and relationships. • Optimized for read performance
- 17. Question: What are a Patron’s Addresses?
- 18. A Patron and their Addresses > patron = db.patrons.find({ _id : “bob” }) { _id: “bob", name: “Bob Knowitall", addresses: [ {street: "1 Vernon St.", city: "Newton", …}, {street: "52 Main St.", city: "Boston", …}, ] }
- 19. A Patron and their Addresses > patron = db.patrons.find({ _id : “bob” }) { _id: “bob", name: “Bob Knowitall", addresses: [ {street: "1 Vernon St.", city: "Newton", …}, {street: "52 Main St.", city: "Boston", …}, ] } > patron = db.patrons.find({ _id : “joe” }) { _id: "joe", name: "Joe Bookreader", address: { street: "123 Fake St. ", city: "Faketon", …} }
- 20. Migration Possibilities • Migrate all documents when the schema changes. • Migrate On-Demand – As we pull up a patron’s document, we make the change. – Any patrons that never come into the library never get updated. • Leave it alone – As long as the application knows about both types…
- 21. Question: Who is the publisher of this book?
- 22. Book MongoDB: The Definitive Guide, By Kristina Chodorow and Mike Dirolf Published: 9/24/2010 Pages: 216 Language: English Publisher: O’Reilly Media, CA
- 23. Book with embedded Publisher > book = db.books.find({ _id : “123” }) { _id: “123”, title: "MongoDB: The Definitive Guide", authors: [ "Kristina Chodorow", "Mike Dirolf" ], published_date: ISODate("2010-09-24"), pages: 216, language: "English", publisher: { name: "O’Reilly Media", founded: "1980", location: "CA" } }
- 24. Book with embedded Publisher • Optimized for read performance of Books • Other queries become difficult
- 25. Question: Who are all the publishers in the system?
- 26. All Publishers > publishers = db.publishers.find() { _id: “oreilly”, name: "O’Reilly Media", founded: "1980", location: "CA" } { _id: “penguin”, name: “Penguin”, founded: “1983”, location: “CA” }
- 27. Book with linked Publisher > book = db.books.find({ _id: “123” }) { _id: “123”, publisher_id: “oreilly”, title: "MongoDB: The Definitive Guide", authors: [ "Kristina Chodorow", "Mike Dirolf" ], published_date: ISODate("2010-09-24"), pages: 216, language: "English" } > db.publishers.find({ _id : book.publisher_id }) { _id: “oreilly”, name: "O’Reilly Media", founded: "1980", location: "CA" }
- 28. Question: What are all the books a publisher has published?
- 29. Publisher with linked Books > publisher = db.publishers.find({ _id : “oreilly” }) { _id: “oreilly”, name: "O’Reilly Media", founded: "1980", location: "CA“, books: [“123”,…] } > books = db.books.find({ _id: { $in : publisher.books } })
- 30. Question: Who are the authors of a given book?
- 31. Books with linked Authors > book = db.books.find({ _id : “123” }) { _id: “123”, title: "MongoDB: The Definitive Guide", published_date: ISODate("2010-09-24"), pages: 216, language: "English“, authors: [“kchodorow”, “mdirolf”] } > authors = db.authors.find({ _id : { $in : book.authors } }) { _id: "kchodorow", name: "Kristina Chodorow”, hometown: … } { _id: “mdirolf", name: “Mike Dirolf“, hometown: … }
- 32. Books with linked Authors > book = db.books.find({ _id : “123” }) { _id: “123”, title: "MongoDB: The Definitive Guide", published_date: ISODate("2010-09-24"), pages: 216, language: "English“, authors = [ { id: "kchodorow", name: "Kristina Chodorow” }, { id: "mdirolf", name: "Mike Dirolf” } ] }
- 33. Question: What are all the books an author has written?
- 34. Authors with linked Books > authors = db.authors.find({ _id : “kchodorow” }) { _id: "kchodorow", name: "Kristina Chodorow", hometown: "Cincinnati", books: [ {id: “123”, title : "MongoDB: The Definitive Guide“ } ] }
- 35. Links on both Authors and Books > authors = db.authors.find({ _id : “kchodorow” }) { _id: "kchodorow", name: "Kristina Chodorow", hometown: "Cincinnati", books: [ {id: “123”, title : "MongoDB: The Definitive Guide“ } ] } > book = db.books.find({ _id : “123” }) { _id: “123”, title: "MongoDB: The Definitive Guide", authors = [ { id: "kchodorow", name: "Kristina Chodorow” }, { id: "mdirolf", name: "Mike Dirolf” } ] }
- 36. Linking vs. Embedding • Embedding – Great for read performance – Writes can be slow – Data integrity needs to be managed • Linking – Flexible – Data integrity is built-in – Work is done during reads
- 37. Question: What are all the books about databases?
- 38. Categories as Documents > book = db.books.find({ _id : “123” }) { _id: “123”, title: "MongoDB: The Definitive Guide", category: “MongoDB” } > categories = db.categories.find({ _id: “MongoDB” }) { _id: “MongoDB”, parent: “Databases” }
- 39. Categories as an Array > book = db.books.find({ _id : “123” }) { _id: “123”, title: "MongoDB: The Definitive Guide", categories: [“MongoDB”, “Databases”, “Programming”] } > db.books.find({ categories: “Databases” })
- 40. Categories as a Path > book = db.books.find({ _id : “123” }) { _id: “123”, title: "MongoDB: The Definitive Guide", category: “Programming/Databases/MongoDB” } > db.books.find({ category: ^Programming/Databases/* })
- 41. Conclusion • Schema design is different in MongoDB • Basic data design principals stay the same • Focus on how an application accesses/manipulates data • Evolve the schema to meet requirements as they change
- 42. #MongoDBDays Schema Design Craig Wilson Software Engineer, 10gen @craiggwilson