good enough

Author: James Halliday

leveldb.markdown

@@ -53,6 +53,8 @@ var db = level('./whatever.db');
 ---
 # put
 
+set a value for a key with `.put()`
+
 ``` js
 var level = require('level');
 var db = level('./whatever.db');
@@ -64,6 +66,8 @@ db.put('key', 'value', function (err) {
 ---
 # get
 
+load a value for a key with `.get()`
+
 ``` js
 var level = require('level');
 var db = level('./whatever.db');
@@ -76,9 +80,30 @@ db.get('key', function (err, value) {
 ---
 # del
 
+delete a value at a key with `.del()`:
+
+---
+# atomicity
+
+either all transactions succeed
+or all transactions fail
+
+---
+# consistency
+
+atomicity is important to enforce consistency
+
+Suppose a user has just signed up.
+We might need to create:
+
+* a record for their 
+* a record for their login username and password
+
 ---
 # batch
 
+perform multiple 
+
 ``` js
 ```
 
@@ -88,25 +113,196 @@ db.get('key', function (err, value) {
 ---
 # thinking lexicographically
 
+keys are sorted by their string values:
+
+* aaaaa
+* bb
+* ccccc
+
+---
+# numbers get converted into strings!
+
+* "1"
+* "12"
+* "3"
+* "4"
+* "555"
+* "6"
+
+---
+# bytewise
+
+a nicer way of handling lexicographic values
+
+sorting for numbers happens as you might expect:
+
+* 1
+* 3
+* 4
+* 6
+* 12
+* 555
+
+---
+# bytewise hierarchy
+
+and there is also a hierarchy of types.
+`null` is the first type to sort and `undefined` is the
+last.
+
+* null
+* numbers
+* strings
+* arrays
+* objects
+* undefined
+
+---
+# bytewise
+
+Arrays are sorted component-wise, which means we can make
+keys like:
+
+    [ 'user', 'substack' ]
+
+and then to query all users we can do:
+
+``` js
+db.createReadStream({
+    gt: [ 'user', null ],
+    lt: [ 'user', undefined ]
+})
+```
+
 ---
 # organizing your keys
 
+key/value structure we might use for
+a user/post system:
+
+``` json
+[{"key":"user!substack","value":{"bio":"beep boop"}},
+{"key":"user!maxogden","value":{"bio":"cats."}},
+{"key":"post!substack!2015-01-04 11:45","value":"cool beans"}]
+{"key":"post!maxogden!2015-01-03 17:33","value":"soup."}]
+```
+
+---
+
+This will let us efficiently query for a user's posts:
+
+``` js
+db.createReadStream({
+    gt: "user!substack",
+    lt: "user!substack!~"
+})
+```
+
+---
+# organizing keys with bytewise
+
+or with bytewise:
+
+``` json
+[{"key":["user","substack"],"value":{"bio":"beep boop"}},
+{"key":["user","maxogden"],"value":{"bio":"cats."}},
+{"key":["post","substack","2015-01-04 11:45"],"value":"cool beans"}]
+{"key":["post","maxogden","2015-01-03 17:33"],"value":"soup."}]
+```
+
+---
+# and querying with bytewise:
+
+``` js
+db.createReadStream({
+    gt: ["user","substack",null],
+    lt: ["user","substack",undefined]
+})
+```
+
+---
+
+In either case,
+what if we want to get ALL the posts on the system?
+
 ---
 # secondary indexes
 
+We can use `.batch()` to create multiple keys for each post:
+
+``` js
+var now = new Date().toISOString();
+var id = crypto.randomBytes(16).toString('hex');
+var subkey = now + '!' + id;
+db.batch([
+    {type:'post',key:'post!substack!'+subkey,value:msg},
+    {type:'post',key:'post!'+subkey,value:msg},
+]);
+```
+
 ---
-# bytewise
+# querying our indexes
+
+now to get all the posts system-wide sorted by date,
+we can do:
+
+``` js
+db.createReadStream({
+    start: "post!",
+    end: "post!~"
+})
+```
 
 ---
 # subleveldown
 
+we can create nested sub-databases with subleveldown:
+
+``` js
+var level = require('level');
+var sublevel = require('subleveldown');
+var db = level('whatever.db');
+
+var catsdb = sublevel(db, 'cats');
+var robodb = sublevel(db, 'robots');
+
+catsdb.put('msg', 'meow');
+robodb.put('msg', 'beep boop');
+```
+
+and `catsdb` and `robodb` will each key a unique namespace
+for a `msg` key.
+
 ---
 # modularity
 
-* accountdown
-* subleveldown
-* cookie-auth
+Instead of building in a lot of features, in leveldb you can
+use npm to install packages:
+
+* [subleveldown](https://npmjs.org/package/subleveldown)
+* [cookie-auth](https://npmjs.org/package/cookie-auth)
+* [accountdown](https://npmjs.org/package/accountdown)
+* [forkdb](https://npmjs.org/package/forkdb)
+
+---
+# accountdown
+
+Making user accounts is actually surprisingly tricky!
+
+You've got to remember:
+
+* only create a user if the name hasn't been taken
+* hash passwords with a unique salt for each user
+* lock records to prevent account creation race conditions
+* extensibility points for more login methods in the future
+
+---
+# links
+
+* [levelup docs](https://github.com/rvagg/node-levelup)
+* [example leveldb website with accountdown](https://github.com/substack/example-user-website)
 
 ---
-# 
+# homework
 
+http://nodeschool.io/#levelmeup