mirror of
https://github.com/koreader/koreader
synced 2024-11-10 01:10:34 +00:00
71 lines
2.0 KiB
Markdown
71 lines
2.0 KiB
Markdown
Data Store
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==========
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## LuaSettings ##
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TODO
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## DocSettings ##
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TODO
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## SQLite3 ##
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KOReader ships with the SQLite3 library, which is a great embedded database for
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desktop and mobile applications.
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[lua-ljsqlite3][ljsq3] is used to export SQLite3 C interfaces as LUA functions.
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Following is a quick example:
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```lua
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local SQ3 = require("lua-ljsqlite3/init")
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local conn = SQ3.open("/path/to/database.sqlite3")
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-- Execute SQL commands separated by the ';' character:
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conn:exec([[
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-- time is in unit of seconds
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CREATE TABLE IF NOT EXISTS page_read_time(page INTEGER, time INTEGER);
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CREATE TABLE IF NOT EXISTS book_property(title TEXT, author TEXT, language TEXT);
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]])
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-- Prepared statements are supported, with this you can bind different values
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-- to the same statement. Let's set the read time for the first 10 pages in the
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-- book to 5 seconds
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local stmt = conn:prepare("INSERT INTO page_read_time VALUES(?, ?)")
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for i=1,10 do
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stmt:reset():bind(i, 5):step()
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end
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-- Now we can retrieve all read time stats for the first 10 pages:
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local results = conn:exec("SELECT * FROM page_read_time") -- Records are by column.
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-- Access to results via column numbers or names:
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assert(results[1] == results.page)
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assert(results[2] == results.time)
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-- Nested indexing corresponds to the record(row) number, access value for 4th page:
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assert(results[1][4] == 4)
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assert(results[2][4] == 5)
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-- access value for 2nd page:
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assert(results.page[2] == 2)
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assert(results.time[2] == 5)
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-- Convenience function returns multiple values for one record:
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local page, time = conn:rowexec("SELECT * FROM page_read_time WHERE page==3")
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print(page, time) --> 3 5
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-- We can also use builtin aggregate functions to do simple analytic task
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local total_time = conn:rowexec("SELECT SUM(time) FROM page_read_time")
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print(total_time) --> 50
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conn:close() -- Do not forget to close stmt after you are done
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```
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For more information on supported SQL quries, check out [SQLite3's official
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documentation][sq3-doc].
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[ljsq3]:http://scilua.org/ljsqlite3.html
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[sq3-doc]:https://www.sqlite.org/docs.html
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