@Column

Customizes a property's column mapping. All parameters are optional — a property without @Column is mapped to a column using its Kotlin property name with no extra constraints.

Signature

@Target(AnnotationTarget.PROPERTY)
@Retention(AnnotationRetention.SOURCE)
annotation class Column(
    val name: String = "",
    val unique: Boolean = false,
    val index: Boolean = false,
    val migrateFrom: String = ""
)

Parameters

Parameter	Type	Default	Description
name	String	""	Overrides the SQLite column name. If empty, the Kotlin property name is used as-is.
unique	Boolean	false	Adds a UNIQUE constraint on this column.
index	Boolean	false	Generates CREATE INDEX IF NOT EXISTS for this column.
migrateFrom	String	""	Migration rename hint. See Auto-migration.

---

name — Override the column name

Use this to set snake_case column names (SQLite convention) for camelCase Kotlin properties.

@DbEntity(tableName = "users")
data class User(
    @PrimaryKey(autoGenerate = true) val id: Long = 0,
    val fullName: String,                               // column: "fullName"
    @Column(name = "full_name") val fullName2: String,  // column: "full_name"
    @Column(name = "created_at") val createdAt: String  // column: "created_at"
)

---

unique — Unique constraint

Generates UNIQUE in the CREATE TABLE statement. Inserting a duplicate value throws a SQLiteConstraintException.

@DbEntity(tableName = "users")
data class User(
    @PrimaryKey(autoGenerate = true) val id: Long = 0,
    @Column(unique = true) val email: String   // UNIQUE
)

---

index — Create an index

Generates CREATE INDEX IF NOT EXISTS idx_<table>_<column> ON <table>("<column>") when createTable() is called. Use this on:

• Foreign key columns — any column used to filter by a parent entity id.
• Frequently queried columns — columns you regularly use in findWhere or observeWhere.

@DbEntity(tableName = "tasks")
data class Task(
    @PrimaryKey(autoGenerate = true) val id: Long = 0,
    @Column(name = "project_id", index = true) val projectId: Long,  // FK index
    val title: String,
    @Column(index = true) val status: String = "TODO"                 // filter index
)

Tip

Indexes on foreign key columns significantly speed up findWhere { TaskColumns.projectId eq someId }. Without an index, SQLite performs a full table scan for every such query.

---

migrateFrom — Column rename hint

When you rename a property, Kiln would normally treat it as "old column removed, new column added" — losing all existing data. Set migrateFrom to preserve the data across the rename.

// Before
@DbEntity(tableName = "tasks")
data class Task(
    @PrimaryKey(autoGenerate = true) val id: Long = 0,
    val priority: Int = 1       // <-- will be renamed
)

// After — existing "priority" data is carried into "urgency"
@DbEntity(tableName = "tasks")
data class Task(
    @PrimaryKey(autoGenerate = true) val id: Long = 0,
    @Column(migrateFrom = "priority") val urgency: Int = 1
)

See Auto-migration for full details on how the migration is performed.

Remove migrateFrom after the migration is deployed

Once all users have upgraded past the version that carried the rename, remove the migrateFrom hint. Leaving it in place has no effect on a schema that has already been migrated, but it is misleading documentation.