feat: support generated (computed) columns via the generated tag

[h2zi]

What this adds

Support for SQLite STORED generated columns through the generated struct tag, keeping the generation expression separate from the column type. Part of rounding out generated-column support across the GORM drivers (see go-gorm/postgres#345 for the PostgreSQL side, which also covers identity columns). Relates to go-gorm/gorm#7191.

type Product struct {
    ID       uint    `gorm:"primaryKey"`
    Price    float64
    Quantity int
    Total    float64 `gorm:"->;generated:price * quantity"` // real GENERATED ALWAYS AS (price * quantity) STORED
}

• The generated value is taken verbatim as the expression of a STORED generated column (SQLite 3.31+). Commas inside the expression are preserved, so generated:coalesce(a, b) works.
• Combine with -> so GORM treats the column as read-only (SQLite forbids writing generated columns).
• The identity keyword is reserved for identity columns; SQLite has no SQL-standard identity, so generated:identity is left to the existing AUTOINCREMENT handling rather than being mistaken for an expression.

Implementation

DataTypeOf appends the GENERATED ALWAYS AS (...) STORED clause when a computed expression is present; the base column type is computed exactly as before.

Tests & verification

• Unit test TestDataTypeOfGeneratedColumn covers the computed clause, comma-safe expressions, and the reserved identity keyword.
• Verified end-to-end against real SQLite: CREATE TABLE emits "total" real GENERATED ALWAYS AS (price * quantity) STORED, INSERT omits the generated column, the read-back value is correct, and repeated AutoMigrate runs are idempotent.

CREATE TABLE `products` (`id` integer PRIMARY KEY AUTOINCREMENT,`name` text,`price` real,
  `quantity` integer,`total` real GENERATED ALWAYS AS (price * quantity) STORED)

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Adds SQLite support in the GORM SQLite dialector for STORED generated (computed) columns via a generated struct tag by appending the GENERATED ALWAYS AS (...) STORED clause to the column’s SQL type during migration.

Changes:

• Extend Dialector.DataTypeOf to emit ... GENERATED ALWAYS AS (<expr>) STORED when a GENERATED tag setting is present.
• Add parsing helpers to treat identity (optionally with always / by default) as a reserved keyword (i.e., not a computed expression).
• Add unit test coverage for the generated-column datatype rendering behavior.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
sqlite.go	Adds generated-column handling in DataTypeOf and helpers to interpret the generated tag and reserve identity.
generated_test.go	Adds unit tests validating generated-column datatype rendering (including comma-containing expressions and reserved identity).

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