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use std::borrow::Cow;
use toasty_core::{
driver::Capability,
schema::db::{
ColumnsDiff, ColumnsDiffItem, IndicesDiffItem, Schema, SchemaDiff, Table, TablesDiffItem,
},
};
use crate::stmt::{AlterColumnChanges, AlterTable, AlterTableAction, DropTable, Name, Statement};
/// A migration step pairing a DDL [`Statement`] with the [`Schema`] it applies against.
///
/// Each `MigrationStatement` carries a snapshot of the schema at the point where
/// the statement should be serialized. This is necessary because rename and
/// recreation operations modify the schema as they go.
pub struct MigrationStatement<'a> {
statement: Statement,
schema: Cow<'a, Schema>,
}
impl<'a> MigrationStatement<'a> {
fn new(statement: Statement, schema: Cow<'a, Schema>) -> Self {
MigrationStatement { statement, schema }
}
/// Generates migration statements from a [`SchemaDiff`].
///
/// Walks the diff's table, column, and index changes and produces the
/// corresponding DDL statements. On databases that lack `ALTER COLUMN`
/// support (e.g. SQLite), column type changes trigger a full table
/// recreation sequence.
pub fn from_diff(schema_diff: &'a SchemaDiff<'a>, capability: &Capability) -> Vec<Self> {
let mut result = Vec::new();
for table in schema_diff.tables().iter() {
match table {
TablesDiffItem::CreateTable(table) => {
result.push(Self::new(
Statement::create_table(table, capability),
Cow::Borrowed(schema_diff.next()),
));
for index in &table.indices {
result.push(Self::new(
Statement::create_index(index),
Cow::Borrowed(schema_diff.next()),
));
}
}
TablesDiffItem::DropTable(table) => result.push(Self::new(
Statement::drop_table(table),
Cow::Borrowed(schema_diff.previous()),
)),
TablesDiffItem::AlterTable {
previous,
next,
columns,
indices,
..
} => {
let mut schema = Cow::Borrowed(schema_diff.previous());
if previous.name != next.name {
result.push(Self::new(
Statement::alter_table_rename_to(previous, &next.name),
schema.clone(),
));
schema.to_mut().table_mut(previous.id).name = next.name.clone();
}
// Check if any column alteration requires table recreation
// (e.g. SQLite can't alter column type/nullability/auto_increment)
let needs_recreation = !capability.schema_mutations.alter_column_type
&& columns.iter().any(|item| {
matches!(
item,
ColumnsDiffItem::AlterColumn {
previous: prev_col,
next: next_col
} if AlterColumnChanges::from_diff(prev_col, next_col).has_type_change()
)
});
if needs_recreation {
Self::emit_table_recreation(
&mut result,
schema,
previous,
next,
columns,
capability,
);
} else {
Self::emit_column_changes(&mut result, schema, columns, capability);
}
// Indices diff
for item in indices.iter() {
match item {
IndicesDiffItem::CreateIndex(index) => {
result.push(Self::new(
Statement::create_index(index),
Cow::Borrowed(schema_diff.next()),
));
}
IndicesDiffItem::DropIndex(index) => {
result.push(Self::new(
Statement::drop_index(index),
Cow::Borrowed(schema_diff.previous()),
));
}
IndicesDiffItem::AlterIndex { previous, next } => {
result.push(Self::new(
Statement::drop_index(previous),
Cow::Borrowed(schema_diff.previous()),
));
result.push(Self::new(
Statement::create_index(next),
Cow::Borrowed(schema_diff.next()),
));
}
}
}
}
}
}
result
}
fn emit_table_recreation(
result: &mut Vec<Self>,
schema: Cow<'a, Schema>,
previous: &Table,
next: &Table,
columns: &ColumnsDiff<'_>,
capability: &Capability,
) {
let current_name = schema.table(previous.id).name.clone();
let temp_name = format!("_toasty_new_{}", current_name);
// 1. PRAGMA foreign_keys = OFF
result.push(Self::new(
Statement::pragma_disable_foreign_keys(),
schema.clone(),
));
// 2. CREATE TABLE temp with new schema
let temp_schema = {
let mut s = schema.as_ref().clone();
let t = s.table_mut(next.id);
t.name = temp_name.clone();
t.columns = next.columns.clone();
t.primary_key = next.primary_key.clone();
s
};
result.push(Self::new(
Statement::create_table(next, capability),
Cow::Owned(temp_schema),
));
// 3. INSERT INTO temp SELECT ... FROM current
let column_mappings: Vec<(Name, Name)> = next
.columns
.iter()
.filter(|col| {
// Skip added columns (no source data)
!columns
.iter()
.any(|item| matches!(item, ColumnsDiffItem::AddColumn(c) if c.id == col.id))
})
.map(|col| {
let target_name = Name::from(&col.name[..]);
// Check if this column was renamed
let source_name = columns
.iter()
.find_map(|item| match item {
ColumnsDiffItem::AlterColumn {
previous: prev_col,
next: next_col,
} if next_col.id == col.id && prev_col.name != next_col.name => {
Some(Name::from(&prev_col.name[..]))
}
_ => None,
})
.unwrap_or_else(|| Name::from(&col.name[..]));
(target_name, source_name)
})
.collect();
result.push(Self::new(
Statement::copy_table(
Name::from(current_name.as_str()),
Name::from(temp_name.as_str()),
column_mappings,
),
schema.clone(),
));
// 4. DROP TABLE current
result.push(Self::new(
DropTable {
name: Name::from(current_name.as_str()),
if_exists: false,
}
.into(),
schema.clone(),
));
// 5. ALTER TABLE temp RENAME TO current
result.push(Self::new(
AlterTable {
name: Name::from(temp_name.as_str()),
action: AlterTableAction::RenameTo(Name::from(current_name.as_str())),
}
.into(),
schema.clone(),
));
// 6. PRAGMA foreign_keys = ON
result.push(Self::new(
Statement::pragma_enable_foreign_keys(),
schema.clone(),
));
}
fn emit_column_changes(
result: &mut Vec<Self>,
schema: Cow<'a, Schema>,
columns: &ColumnsDiff<'_>,
capability: &Capability,
) {
for item in columns.iter() {
match item {
ColumnsDiffItem::AddColumn(column) => {
result.push(Self::new(
Statement::add_column(column, capability),
schema.clone(),
));
}
ColumnsDiffItem::DropColumn(column) => {
result.push(Self::new(Statement::drop_column(column), schema.clone()));
}
ColumnsDiffItem::AlterColumn {
previous,
next: col_next,
} => {
let changes = AlterColumnChanges::from_diff(previous, col_next);
let changes = if capability.schema_mutations.alter_column_properties_atomic {
vec![changes]
} else {
changes.split()
};
for changes in changes {
result.push(Self::new(
Statement::alter_column(previous, changes, capability),
schema.clone(),
));
}
}
}
}
}
/// Returns the DDL statement for this migration step.
pub fn statement(&self) -> &Statement {
&self.statement
}
/// Returns the schema snapshot this statement should be serialized against.
pub fn schema(&self) -> &Schema {
&self.schema
}
}