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Automatically set PRAGMAs using connection query params (#85 )

* Automatically set PRAGMAs using connection query params

Introduce the flexibility to adjust certain PRAGMAs of the SQLite3
connection without having to hardcode those in your codebase (and wait
for compilation).

This allows applications to use `DATABASE_URL` to dynamically fine tune
their SQLite3 configuration.

The change complements `#setup_connection` that offers, via code, the
option to perform queries on setup of each connection.

Only a few PRAGMAs necessary to allow more performant concurrent reads
and reduce write locking.

These pragmas are detected and combined in a single SQL string to reduce
to 1 the number of calls to `sqlite3_exec` C function.

There is no validation of supplied values as SQLite3 automatically
ignores incorrect values for these pragmas.

Closes #84

References:
- https://www.sqlite.org/pragma.html

* Simplify PRAGMA mapping and detection

No longer prefix PRAGMAS with `_`, so the mapping between the real
SQLite3 pragmas and the usage in the URI is more direct.

Use macros instead of case to detect pragmas from URI params and return
those as NamedTuple.

* Update README.md

---------

Co-authored-by: Brian J. Cardiff <bcardiff@gmail.com>

2023-02-18 17:06:09 -03:00

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crystal-sqlite3

SQLite3 bindings for Crystal.

Check crystal-db for general db driver documentation. crystal-sqlite3 driver is registered under sqlite3:// uri.

Installation

Add this to your application's shard.yml:

dependencies:
  sqlite3:
    github: crystal-lang/crystal-sqlite3

Usage

require "sqlite3"

DB.open "sqlite3://./data.db" do |db|
  db.exec "create table contacts (name text, age integer)"
  db.exec "insert into contacts values (?, ?)", "John Doe", 30

  args = [] of DB::Any
  args << "Sarah"
  args << 33
  db.exec "insert into contacts values (?, ?)", args: args

  puts "max age:"
  puts db.scalar "select max(age) from contacts" # => 33

  puts "contacts:"
  db.query "select name, age from contacts order by age desc" do |rs|
    puts "#{rs.column_name(0)} (#{rs.column_name(1)})"
    # => name (age)
    rs.each do
      puts "#{rs.read(String)} (#{rs.read(Int32)})"
      # => Sarah (33)
      # => John Doe (30)
    end
  end
end

DB::Any

Time is implemented as TEXT column using SQLite3::DATE_FORMAT_SUBSECOND format (or SQLite3::DATE_FORMAT_SECOND if the text does not contain a dot).
Bool is implemented as INT column mapping 0/1 values.

Setting PRAGMAs

You can adjust certain SQLite3 PRAGMAs automatically when the connection is created by using the query parameters:

require "sqlite3"

DB.open "sqlite3://./data.db?journal_mode=wal&synchronous=normal" do |db|
  # this database now uses WAL journal and normal synchronous mode
  # (defaults were `delete` and `full`, respectively)
end

The following is the list of supported options:

Name	Connection key
Busy Timeout	`busy_timeout`
Cache Size	`cache_size`
Foreign Keys	`foreign_keys`
Journal Mode	`journal_mode`
Synchronous	`synchronous`
WAL autocheckoint	`wal_autocheckpoint`

Please note there values passed using these connection keys are passed directly to SQLite3 without check or evaluation. Using incorrect values result in no error by the library.