mirror of https://github.com/koreader/koreader
doc: add sqlite sample code
parent
88ab21c62c
commit
42d74c0a36
@ -0,0 +1,73 @@
|
||||
Data Store
|
||||
==========
|
||||
|
||||
LuaSettings
|
||||
-----------
|
||||
|
||||
TODO
|
||||
|
||||
|
||||
DocSettings
|
||||
-----------
|
||||
|
||||
TODO
|
||||
|
||||
|
||||
SQLite3
|
||||
-------
|
||||
|
||||
KOReader ships with the SQLite3 library, which is a great embedded database for
|
||||
desktop and mobile applications.
|
||||
|
||||
[lua-ljsqlite3][ljsq3] is used to export SQLite3 C interfaces as LUA functions.
|
||||
Following is a quick example:
|
||||
|
||||
```lua
|
||||
local SQ3 = require("lua-ljsqlite3/init")
|
||||
|
||||
local conn = SQ3.open("/path/to/database.sqlite3")
|
||||
|
||||
-- Execute SQL commands separated by the ';' character:
|
||||
conn:exec([[
|
||||
-- time is in unit of seconds
|
||||
CREATE TABLE IF NOT EXISTS page_read_time(page INTEGER, time INTEGER);
|
||||
CREATE TABLE IF NOT EXISTS book_property(title TEXT, author TEXT, language TEXT);
|
||||
]])
|
||||
|
||||
-- Prepared statements are supported, with this you can bind different values
|
||||
-- to the same statement. Let's set the read time for the first 10 pages in the
|
||||
-- book to 5 seconds
|
||||
local stmt = conn:prepare("INSERT INTO page_read_time VALUES(?, ?)")
|
||||
for i=1,10 do
|
||||
stmt:reset():bind(i, 5):step()
|
||||
end
|
||||
|
||||
-- Now we can retrieve all read time stats for the first 10 pages:
|
||||
local results = conn:exec("SELECT * FROM page_read_time") -- Records are by column.
|
||||
-- Access to results via column numbers or names:
|
||||
assert(results[1] == results.page)
|
||||
assert(results[2] == results.time)
|
||||
-- Nested indexing corresponds to the record(row) number, access value for 4th page:
|
||||
assert(results[1][4] == 4)
|
||||
assert(results[2][4] == 5)
|
||||
-- access value for 2nd page:
|
||||
assert(results.page[2] == 2)
|
||||
assert(results.time[2] == 5)
|
||||
|
||||
-- Convenience function returns multiple values for one record:
|
||||
local page, time = conn:rowexec("SELECT * FROM page_read_time WHERE page==3")
|
||||
print(page, time) --> 3 5
|
||||
|
||||
-- We can also use builtin aggregate functions to do simple analytic task
|
||||
local total_time = conn:rowexec("SELECT SUM(time) FROM page_read_time")
|
||||
print(total_time) --> 50
|
||||
|
||||
conn:close() -- Do not forget to close stmt after you are done
|
||||
```
|
||||
|
||||
For more information on supported SQL quries, check out [SQLite3's official
|
||||
documentation][sq3-doc].
|
||||
|
||||
|
||||
[ljsq3]:http://scilua.org/ljsqlite3.html
|
||||
[sq3-doc]:https://www.sqlite.org/docs.html
|
Loading…
Reference in New Issue