feat: add @generated attribute for stored generated columns (PostgreSQL)

libs/sql-ddl/src/postgres.rs

@@ -72,6 +72,9 @@ pub struct Column<'a> {
     pub name: Cow<'a, str>,
     pub r#type: Cow<'a, str>,
     pub default: Option<Cow<'a, str>>,
+    /// SQL expression for a generated (computed) column.
+    /// When set, renders as `GENERATED ALWAYS AS (expr) STORED` instead of a DEFAULT clause.
+    pub generation_expression: Option<Cow<'a, str>>,
 }
 
 impl Display for Column<'_> {
@@ -80,7 +83,11 @@ impl Display for Column<'_> {
         f.write_str(" ")?;
         f.write_str(self.r#type.as_ref())?;
 
-        if let Some(default) = &self.default {
+        if let Some(expr) = &self.generation_expression {
+            f.write_str(" GENERATED ALWAYS AS (")?;
+            f.write_str(expr)?;
+            f.write_str(") STORED")?;
+        } else if let Some(default) = &self.default {
             f.write_str(" DEFAULT ")?;
             f.write_str(default)?;
         }
@@ -545,4 +552,47 @@ mod tests {
 
         assert_eq!(alter_table.to_string(), expected);
     }
+
+    #[test]
+    fn column_with_generation_expression() {
+        let col = Column {
+            name: "status_priority".into(),
+            r#type: "INT".into(),
+            default: None,
+            generation_expression: Some("CASE status WHEN 'A' THEN 1 WHEN 'B' THEN 2 END".into()),
+        };
+
+        assert_eq!(
+            col.to_string(),
+            r#""status_priority" INT GENERATED ALWAYS AS (CASE status WHEN 'A' THEN 1 WHEN 'B' THEN 2 END) STORED"#
+        );
+    }
+
+    #[test]
+    fn column_with_generation_expression_takes_precedence_over_default() {
+        let col = Column {
+            name: "computed".into(),
+            r#type: "TEXT".into(),
+            default: Some("'fallback'".into()),
+            generation_expression: Some("first || ' ' || last".into()),
+        };
+
+        // generation_expression should win over default
+        assert_eq!(
+            col.to_string(),
+            r#""computed" TEXT GENERATED ALWAYS AS (first || ' ' || last) STORED"#
+        );
+    }
+
+    #[test]
+    fn column_without_generation_expression_renders_default() {
+        let col = Column {
+            name: "name".into(),
+            r#type: "TEXT".into(),
+            default: Some("'unknown'".into()),
+            generation_expression: None,
+        };
+
+        assert_eq!(col.to_string(), r#""name" TEXT DEFAULT 'unknown'"#);
+    }
 }

psl/parser-database/src/attributes.rs

@@ -188,6 +188,21 @@ fn resolve_model_attributes(model_id: crate::ModelId, ctx: &mut Context<'_>) {
     id::validate_id_field_arities(model_id, &model_attributes, ctx);
     shard_key::validate_shard_key_field_arities(model_id, &model_attributes, ctx);
 
+    // Validate that generated columns are not part of the primary key (@@id or @id).
+    if let Some(pk) = &model_attributes.primary_key {
+        for pk_field in &pk.fields {
+            let sfid = pk_field.path.root();
+            if ctx.types[sfid].is_generated_column {
+                let ast_field = &ctx.asts[ctx.types[sfid].model_id][ctx.types[sfid].field_id];
+                ctx.push_error(DatamodelError::new_attribute_validation_error(
+                    "Fields that are marked with @generated cannot be part of the primary key (@id or @@id).",
+                    "@generated",
+                    ast_field.span(),
+                ));
+            }
+        }
+    }
+
     ctx.types.model_attributes.insert(model_id, model_attributes);
     ctx.validate_visited_attributes();
 }
@@ -249,6 +264,26 @@ fn visit_scalar_field_attributes(
         ctx.validate_visited_arguments();
     }
 
+    // @generated("sql expression")
+    if ctx.visit_optional_single_attr("generated") {
+        if ast_field.arity.is_list() {
+            ctx.push_attribute_validation_error("Fields that are marked with @generated cannot be lists.");
+        }
+
+        match ctx.visit_default_arg("expression") {
+            Ok(expr) => {
+                if let Some((expr_str, _span)) = expr.as_string_value() {
+                    ctx.types[scalar_field_id].is_generated_column = true;
+                    ctx.types[scalar_field_id].generation_expression = Some(expr_str.to_owned());
+                } else {
+                    ctx.push_attribute_validation_error("The @generated attribute requires a string argument with the SQL expression.");
+                }
+            }
+            Err(err) => ctx.push_error(err),
+        }
+        ctx.validate_visited_arguments();
+    }
+
     // @default
     if ctx.visit_optional_single_attr("default") {
         default::visit_model_field_default(scalar_field_id, model_id, field_id, r#type, ctx);
@@ -281,6 +316,26 @@ fn visit_scalar_field_attributes(
         ctx.validate_visited_arguments();
     }
 
+    // Cross-attribute validations for @generated
+    if ctx.types[scalar_field_id].is_generated_column {
+        if ctx.types[scalar_field_id].default.is_some() {
+            ctx.push_error(DatamodelError::new_attribute_validation_error(
+                "Fields that are marked with @generated cannot have a @default value. The column value is always computed from the generation expression.",
+                "@generated",
+                ast_field.span(),
+            ));
+        }
+        if ctx.types[scalar_field_id].is_updated_at {
+            ctx.push_error(DatamodelError::new_attribute_validation_error(
+                "Fields that are marked with @generated cannot also be marked with @updatedAt.",
+                "@generated",
+                ast_field.span(),
+            ));
+        }
+        // Note: @generated + primary key (@id / @@id) is validated at model level
+        // in resolve_model_attributes(), after @@id has been processed.
+    }
+
     ctx.validate_visited_attributes();
 }
 

psl/parser-database/src/types.rs

@@ -328,6 +328,9 @@ pub(crate) struct ScalarField {
     pub(crate) r#type: ScalarFieldType,
     pub(crate) is_ignored: bool,
     pub(crate) is_updated_at: bool,
+    pub(crate) is_generated_column: bool,
+    /// The SQL expression for a generated (computed) column, e.g. "CASE status WHEN 'A' THEN 1 END"
+    pub(crate) generation_expression: Option<String>,
     pub(crate) default: Option<DefaultAttribute>,
     /// @map
     pub(crate) mapped_name: Option<StringId>,
@@ -759,6 +762,8 @@ fn visit_model<'db>(model_id: crate::ModelId, ast_model: &'db ast::Model, ctx: &
                     r#type: scalar_field_type,
                     is_ignored: false,
                     is_updated_at: false,
+                    is_generated_column: false,
+                    generation_expression: None,
                     default: None,
                     mapped_name: None,
                     native_type: None,

psl/parser-database/src/walkers/scalar_field.rs

@@ -115,6 +115,16 @@ impl<'db> ScalarFieldWalker<'db> {
         self.attributes().is_updated_at
     }
 
+    /// Is this a generated (computed) column?
+    pub fn is_generated_column(self) -> bool {
+        self.attributes().is_generated_column
+    }
+
+    /// The SQL expression for a generated column, if any.
+    pub fn generation_expression(self) -> Option<&'db str> {
+        self.attributes().generation_expression.as_deref()
+    }
+
     fn attributes(self) -> &'db ScalarField {
         &self.db.types[self.id]
     }

psl/psl-core/src/common/preview_features.rs

@@ -56,6 +56,7 @@ features!(
     FullTextIndex,
     FullTextSearch,
     FullTextSearchPostgres,
+    GeneratedColumns,
     GroupBy,
     ImprovedQueryRaw,
     InteractiveTransactions,
@@ -157,7 +158,8 @@ impl<'a> FeatureMapWithProvider<'a> {
         // Generator preview features (alphabetically sorted)
         let feature_map: FeatureMap = FeatureMap {
             active: enumflags2::make_bitflags!(PreviewFeature::{
-                 NativeDistinct
+                 GeneratedColumns
+                 | NativeDistinct
                  | PartialIndexes
                  | PostgresqlExtensions
                  | RelationJoins

psl/psl-core/src/validate/validation_pipeline/validations.rs

@@ -96,7 +96,8 @@ pub(super) fn validate(ctx: &mut Context<'_>) {
             fields::has_a_unique_default_constraint_name(field, &names, ctx);
             fields::validate_native_type_arguments(field, ctx);
             fields::validate_default_value(field, ctx);
-            fields::validate_unsupported_field_type(field, ctx)
+            fields::validate_unsupported_field_type(field, ctx);
+            fields::validate_generated_column(field, ctx);
         }
 
         for field in model.relation_fields() {

psl/psl-core/src/validate/validation_pipeline/validations/fields.rs

@@ -419,3 +419,32 @@ pub(crate) fn clustering_can_be_defined_only_once(pk: PrimaryKeyWalker<'_>, ctx:
         return;
     }
 }
+
+pub(super) fn validate_generated_column(field: ScalarFieldWalker<'_>, ctx: &mut Context<'_>) {
+    use crate::datamodel_connector::Flavour;
+
+    if !field.is_generated_column() {
+        return;
+    }
+
+    let span = field
+        .ast_field()
+        .span_for_attribute("generated")
+        .unwrap_or_else(|| field.ast_field().span());
+
+    if !ctx.preview_features.contains(crate::PreviewFeature::GeneratedColumns) {
+        ctx.push_error(DatamodelError::new_attribute_validation_error(
+            "Generated columns are a preview feature. Add \"generatedColumns\" to previewFeatures in your generator block.",
+            "@generated",
+            span,
+        ));
+    }
+
+    if !matches!(ctx.connector.flavour(), Flavour::Postgres) {
+        ctx.push_error(DatamodelError::new_attribute_validation_error(
+            "Generated columns are not supported by the current connector. Currently only PostgreSQL supports @generated.",
+            "@generated",
+            span,
+        ));
+    }
+}

psl/psl/tests/attributes/generated_negative.rs

@@ -0,0 +1,139 @@
+use crate::{Provider, common::*, with_header};
+
+#[test]
+fn should_fail_without_preview_feature() {
+    let dml = indoc! {r#"
+        model User {
+          id   Int    @id
+          calc Int?   @generated("id * 2")
+        }
+    "#};
+
+    // No "generatedColumns" in preview features
+    let error = parse_unwrap_err(&with_header(dml, Provider::Postgres, &[]));
+
+    assert!(error.contains("preview feature"));
+    assert!(error.contains("generatedColumns"));
+}
+
+#[test]
+fn should_fail_without_expression_argument() {
+    let dml = indoc! {r#"
+        model User {
+          id   Int    @id
+          name String @generated
+        }
+    "#};
+
+    let error = parse_unwrap_err(&with_header(dml, Provider::Postgres, &["generatedColumns"]));
+
+    assert!(error.contains("@generated"));
+    assert!(error.contains("Argument"));
+}
+
+#[test]
+fn should_fail_with_non_string_argument() {
+    let dml = indoc! {r#"
+        model User {
+          id   Int @id
+          calc Int @generated(42)
+        }
+    "#};
+
+    let error = parse_unwrap_err(&with_header(dml, Provider::Postgres, &["generatedColumns"]));
+
+    assert!(error.contains("@generated"));
+    assert!(error.contains("string"));
+}
+
+#[test]
+fn should_fail_when_combined_with_default() {
+    let dml = indoc! {r#"
+        model User {
+          id   Int    @id
+          calc Int?   @generated("id * 2") @default(0)
+        }
+    "#};
+
+    let error = parse_unwrap_err(&with_header(dml, Provider::Postgres, &["generatedColumns"]));
+
+    assert!(error.contains("@generated"));
+    assert!(error.contains("@default"));
+}
+
+#[test]
+fn should_fail_when_combined_with_updated_at() {
+    let dml = indoc! {r#"
+        model User {
+          id   Int      @id
+          ts   DateTime @generated("now()") @updatedAt
+        }
+    "#};
+
+    let error = parse_unwrap_err(&with_header(dml, Provider::Postgres, &["generatedColumns"]));
+
+    assert!(error.contains("@generated"));
+    assert!(error.contains("@updatedAt"));
+}
+
+#[test]
+fn should_fail_when_combined_with_id() {
+    let dml = indoc! {r#"
+        model User {
+          id   Int @id @generated("1")
+          name String
+        }
+    "#};
+
+    let error = parse_unwrap_err(&with_header(dml, Provider::Postgres, &["generatedColumns"]));
+
+    assert!(error.contains("@generated"));
+    assert!(error.contains("@id"));
+}
+
+#[test]
+fn should_fail_when_part_of_compound_id() {
+    let dml = indoc! {r#"
+        model User {
+          a    Int
+          b    Int @generated("a * 2")
+
+          @@id([a, b])
+        }
+    "#};
+
+    let error = parse_unwrap_err(&with_header(dml, Provider::Postgres, &["generatedColumns"]));
+
+    assert!(error.contains("@generated"));
+    assert!(error.contains("@@id"));
+}
+
+#[test]
+fn should_fail_on_list_field() {
+    let dml = indoc! {r#"
+        model User {
+          id    Int   @id
+          tags  Int[] @generated("ARRAY[1,2,3]")
+        }
+    "#};
+
+    let error = parse_unwrap_err(&with_header(dml, Provider::Postgres, &["generatedColumns"]));
+
+    assert!(error.contains("@generated"));
+    assert!(error.contains("list"));
+}
+
+#[test]
+fn should_fail_on_unsupported_connector() {
+    let dml = indoc! {r#"
+        model User {
+          id   Int  @id
+          calc Int? @generated("id * 2")
+        }
+    "#};
+
+    let error = parse_unwrap_err(&with_header(dml, Provider::Mysql, &["generatedColumns"]));
+
+    assert!(error.contains("@generated"));
+    assert!(error.contains("not supported"));
+}