howdah - an application using pylons, postgresql, simpycity and exceptable

HOWDAHA tutorial

Tuesday, October 20, 2009

Why?

Howdah is for people who really “get” databases

Howdah treats your database as code. Procedures, and hand-written SQL.

Would you automate python generation? Then why SQL?

Just because it’s not code you’re comfortable with, doesn’t make it any less code.

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What shall we build?

Today, we’ll be talking about designing and implementing a Wiki.

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Why a Wiki?

Canonical example

Simple enough to define in an afternoon

Complex enough to require in-depth exploration

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Why a Wiki?

Public and Private permissions/users

Read/write collaborative model

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Design vs. Code

Speaking more on Design than on Code

Why is more important than How.

How is still important

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STEP 1:DESIGN

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Database

What do we need?

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Application

What do we need?

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Application

What do we need?

Anything else? Did we miss anything?

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STEP 2:REVISIT

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Database

Based on our Application design, what expansions do we need?

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Database

Based on our Application design, what expansions do we need?

Why do we need them?

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Application

With the new DB features, what changes?

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Application


What new ideas are evident?

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Application


What new ideas are evident?

Do the changes make things easier?

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STEP 3:API CONTRACTS

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DatabaseDefining our API

What stored procedures do we need?

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What stored procedures do we need?

What should they do?

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What exceptions do we need?

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Null data

Bad data

No such record

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ApplicationDefining our API

What models do we need?

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What do DB exceptions become?

What HTTP responses should the exceptions raise?

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What views do we need?

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What views are read-only? Read-write? Write-only?

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STEP 4:FIRST EXPANSION

USERS

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DatabaseUsers

User system!

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DatabaseUsers

User system!

VerticallyChallenged for users

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DatabaseUsers

User system!

VerticallyChallenged for users

How to set up VC

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DatabaseUsers

Stored Procedures - How do we adapt them?

How does this affect our API contract?

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ApplicationUsers

Using @needs to define permissions

How should views be protected?

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ApplicationUsers

Using @needs to define permissions

How should views be protected?

Should anonymous users have write permission?

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ApplicationUsers

Permissions violations

What should no user return?

What should a bad user return?

What should insufficient permissions return?

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ApplicationUsers

Why - Are there better mechanisms?

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STEP 5:ADMINISTRATIVE

USERS

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DatabaseAdministrators

What delineates an admin?

What special things can an admin do?

Should admins be otherwise normal users?

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Root-level permissions:

Should the database superuser ever be allowed to log in from the web app?

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Root-level permissions:

Should the database superuser ever be allowed to log in from the web app?

Why?

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ApplicationAdministrators

What delineates an Admin?

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Design

Are there special admin-only views?

How do we protect admin privileges?

Are there user-specific views? Do admins have permission to access those?

Is anything changed by the DB layer?

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Should administrators be able to view everything?

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What about privileged information?

HIPAA, lawyer confidentiality

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What about privileged information?

HIPAA, lawyer confidentiality

How can we protect privileged information like this?

Can we ever guarantee protection? How?

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STEP 6:A NEW FEATURE

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A New Feature

Let’s add a user profile page

Specifically list the pages that a user has edited

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DatabaseA New Feature

Design first!

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DatabaseA New Feature

Design first!

Do we need new stored procedures?

What are they?

Who has access to them?

Does this require write access?

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ApplicationA New Feature

What does the app need to support this?

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Who has access to the views?

Logged-in users only?

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What about security and data confidentiality?

What security issues could be present?

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Do we list entries that a user may not have read access to?

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Do we list entries that a user may not have read access to?

Should we list nothing, instead?

Why do it like this? Are there better solutions?

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howdah - an application using pylons, postgresql, simpycity and exceptable

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application dening

database dening

application design

application usersusing

application userswhy

application administratorswhat

database superuser

apiwhat views