Started working on qu unit conversion handling (references #177)

migrations/0082.sql

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+CREATE TABLE quantity_unit_conversions (
+	id INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT UNIQUE,
+	from_qu_id INT NOT NULL,
+	to_qu_id INT NOT NULL,
+	factor REAL NOT NULL,
+	product_id INT,
+	row_created_timestamp DATETIME DEFAULT (datetime('now', 'localtime'))
+);
+
+CREATE TRIGGER quantity_unit_conversions_custom_unique_constraint_INS BEFORE INSERT ON quantity_unit_conversions
+BEGIN
+-- Necessary because unique constraints don't include NULL values in SQLite, and also because the constraint should include the products default conversion factor
+SELECT CASE WHEN((
+	SELECT 1
+	FROM quantity_unit_conversions
+	WHERE from_qu_id = NEW.from_qu_id
+		AND to_qu_id = NEW.to_qu_id
+		AND IFNULL(product_id, 0) = IFNULL(NEW.product_id, 0)
+	UNION
+	SELECT 1
+	FROM products
+	WHERE id = NEW.product_id
+		AND qu_id_purchase = NEW.from_qu_id
+		AND qu_id_stock = NEW.to_qu_id
+	)
+	NOTNULL) THEN RAISE(ABORT, "Unique constraint violation") END;
+END;
+
+CREATE TRIGGER quantity_unit_conversions_custom_unique_constraint_UPD BEFORE UPDATE ON quantity_unit_conversions
+BEGIN
+-- Necessary because unique constraints don't include NULL values in SQLite, and also because the constraint should include the products default conversion factor
+SELECT CASE WHEN((
+	SELECT 1
+	FROM quantity_unit_conversions
+	WHERE from_qu_id = NEW.from_qu_id
+		AND to_qu_id = NEW.to_qu_id
+		AND IFNULL(product_id, 0) = IFNULL(NEW.product_id, 0)
+	UNION
+	SELECT 1
+	FROM products
+	WHERE id = NEW.product_id
+		AND qu_id_purchase = NEW.from_qu_id
+		AND qu_id_stock = NEW.to_qu_id
+	)
+	NOTNULL) THEN RAISE(ABORT, "Unique constraint violation") END;
+END;
+
+CREATE VIEW quantity_unit_conversions_resolved
+AS
+-- First: Product "purchase to stock" conversion factor
+SELECT
+	p.id AS product_id,
+	p.qu_id_purchase AS from_qu_id,
+	p.qu_id_stock AS to_qu_id,
+	p.qu_factor_purchase_to_stock AS factor
+FROM products p
+
+UNION
+
+-- Second: Product specific overrides
+SELECT
+	p.id AS product_id,
+	p.qu_id_stock AS from_qu_id,
+	quc.to_qu_id AS to_qu_id,
+	quc.factor AS factor
+FROM products p
+JOIN quantity_unit_conversions quc
+	ON p.qu_id_stock = quc.from_qu_id
+	AND p.id = quc.product_id
+
+UNION
+
+-- Third: Default quantity unit conversion factors
+SELECT
+	p.id AS product_id,
+	p.qu_id_stock AS from_qu_id,
+	quc.to_qu_id AS to_qu_id,
+	quc.factor AS factor
+FROM products p
+JOIN quantity_unit_conversions quc
+	ON p.qu_id_stock = quc.from_qu_id
+	AND quc.product_id IS NULL;