Add CHECK constraints to internal schema

Add knowledge of `CHECK` constraints to `pgroll`'s internal schema
representation.

pkg/schema/schema.go

@@ -49,6 +49,9 @@ type Table struct {
 
 	// ForeignKeys is a map of all foreign keys defined on the table
 	ForeignKeys map[string]ForeignKey `json:"foreignKeys"`
+
+	// CheckConstraints is a map of all check constraints defined on the table
+	CheckConstraints map[string]CheckConstraint `json:"checkConstraints"`
 }
 
 type Column struct {
@@ -85,6 +88,17 @@ type ForeignKey struct {
 	ReferencedColumns []string `json:"referencedColumns"`
 }
 
+type CheckConstraint struct {
+	// Name is the name of the check constraint in postgres
+	Name string `json:"name"`
+
+	// The columns that the check constraint is defined on
+	Columns []string `json:"columns"`
+
+	// The definition of the check constraint
+	Definition string `json:"definition"`
+}
+
 func (s *Schema) GetTable(name string) *Table {
 	if s.Tables == nil {
 		return nil

pkg/state/state.go

@@ -173,6 +173,24 @@ BEGIN
 				  FROM pg_index pi 
 				  WHERE pi.indrelid = t.oid::regclass
 				),
+				'checkConstraints', (
+					SELECT json_object_agg(cc_details.conname, json_build_object(
+						'name', cc_details.conname,
+						'columns', cc_details.columns,
+						'definition', cc_details.definition
+					))
+					FROM (
+						SELECT
+							cc_constraint.conname,
+							array_agg(cc_attr.attname ORDER BY cc_constraint.conkey::int[]) AS columns,
+							pg_get_constraintdef(cc_constraint.oid) AS definition
+						FROM pg_constraint AS cc_constraint
+						INNER JOIN pg_attribute cc_attr ON cc_attr.attrelid = cc_constraint.conrelid AND cc_attr.attnum = ANY(cc_constraint.conkey)
+						WHERE cc_constraint.conrelid = t.oid
+						AND cc_constraint.contype = 'c'
+						GROUP BY cc_constraint.oid
+					) AS cc_details
+        ),
 				'foreignKeys', (
 					SELECT json_object_agg(fk_details.conname, json_build_object(
 						'name', fk_details.conname,