Track foreign key ON DELETE setting in the internal schema representation (#311)

Add the `ON DELETE` setting of a foreign key to the information stored
about the key in the internal schema representation.

The schema representation for a foreign key now looks like:

```json
{
  "some_table": {
    ...
    "foreignKeys": {
      "fk_users_id": {
        "name": "fk_users_id",
        "columns": [
          "user_id"
        ],
        "onDelete": "NO ACTION",
        "referencedTable": "users",
        "referencedColumns": [
          "id"
        ]
      }
    }
  }
}
```

Fixes https://github.com/xataio/pgroll/issues/309

pkg/schema/schema.go

@@ -95,6 +95,9 @@ type ForeignKey struct {
 
 	// The columns in the referenced table that the foreign key references
 	ReferencedColumns []string `json:"referencedColumns"`
+
+	// The ON DELETE behavior of the foreign key
+	OnDelete string `json:"onDelete"`
 }
 
 type CheckConstraint struct {

pkg/state/state.go

@@ -223,21 +223,29 @@ BEGIN
 						'name', fk_details.conname,
 						'columns', fk_details.columns,
 						'referencedTable', fk_details.referencedTable,
-						'referencedColumns', fk_details.referencedColumns
+						'referencedColumns', fk_details.referencedColumns,
+						'onDelete', fk_details.onDelete
 					)), '{}'::json)
 					FROM (
 						SELECT
 							fk_constraint.conname,
 							array_agg(fk_attr.attname ORDER BY fk_constraint.conkey::int[]) AS columns,
 							fk_cl.relname AS referencedTable,
-							array_agg(ref_attr.attname ORDER BY fk_constraint.confkey::int[]) AS referencedColumns
+							array_agg(ref_attr.attname ORDER BY fk_constraint.confkey::int[]) AS referencedColumns,
+							CASE
+							  WHEN fk_constraint.confdeltype = 'a' THEN 'NO ACTION'
+							  WHEN fk_constraint.confdeltype = 'r' THEN 'RESTRICT'
+							  WHEN fk_constraint.confdeltype = 'c' THEN 'CASCADE'
+							  WHEN fk_constraint.confdeltype = 'd' THEN 'SET DEFAULT'
+							  WHEN fk_constraint.confdeltype = 'n' THEN 'SET NULL'
+							END as onDelete
 						FROM pg_constraint AS fk_constraint
 						INNER JOIN pg_class fk_cl ON fk_constraint.confrelid = fk_cl.oid
 						INNER JOIN pg_attribute fk_attr ON fk_attr.attrelid = fk_constraint.conrelid AND fk_attr.attnum = ANY(fk_constraint.conkey)
 						INNER JOIN pg_attribute ref_attr ON ref_attr.attrelid = fk_constraint.confrelid AND ref_attr.attnum = ANY(fk_constraint.confkey)
 						WHERE fk_constraint.conrelid = t.oid
 						AND fk_constraint.contype = 'f'
-						GROUP BY fk_constraint.conname, fk_cl.relname
+						GROUP BY fk_constraint.conname, fk_cl.relname, fk_constraint.confdeltype
 					) AS fk_details
 				)
 			)), '{}'::json) FROM pg_class AS t

pkg/state/state_test.go

@@ -471,6 +471,61 @@ func TestReadSchema(t *testing.T) {
 									Columns:           []string{"fk"},
 									ReferencedTable:   "table1",
 									ReferencedColumns: []string{"id"},
+									OnDelete:          "NO ACTION",
+								},
+							},
+							CheckConstraints:  map[string]schema.CheckConstraint{},
+							UniqueConstraints: map[string]schema.UniqueConstraint{},
+						},
+					},
+				},
+			},
+			{
+				name:       "foreign key with ON DELETE CASCADE",
+				createStmt: "CREATE TABLE public.table1 (id int PRIMARY KEY); CREATE TABLE public.table2 (fk int NOT NULL, CONSTRAINT fk_fkey FOREIGN KEY (fk) REFERENCES public.table1 (id) ON DELETE CASCADE)",
+				wantSchema: &schema.Schema{
+					Name: "public",
+					Tables: map[string]schema.Table{
+						"table1": {
+							Name: "table1",
+							Columns: map[string]schema.Column{
+								"id": {
+									Name:     "id",
+									Type:     "integer",
+									Nullable: false,
+									Unique:   true,
+								},
+							},
+							PrimaryKey: []string{"id"},
+							Indexes: map[string]schema.Index{
+								"table1_pkey": {
+									Name:    "table1_pkey",
+									Unique:  true,
+									Columns: []string{"id"},
+								},
+							},
+							CheckConstraints:  map[string]schema.CheckConstraint{},
+							UniqueConstraints: map[string]schema.UniqueConstraint{},
+							ForeignKeys:       map[string]schema.ForeignKey{},
+						},
+						"table2": {
+							Name: "table2",
+							Columns: map[string]schema.Column{
+								"fk": {
+									Name:     "fk",
+									Type:     "integer",
+									Nullable: false,
+								},
+							},
+							PrimaryKey: []string{},
+							Indexes:    map[string]schema.Index{},
+							ForeignKeys: map[string]schema.ForeignKey{
+								"fk_fkey": {
+									Name:              "fk_fkey",
+									Columns:           []string{"fk"},
+									ReferencedTable:   "table1",
+									ReferencedColumns: []string{"id"},
+									OnDelete:          "CASCADE",
 								},
 							},
 							CheckConstraints:  map[string]schema.CheckConstraint{},