func (schema *Schema) ParseUniqueConstraints() map[string]UniqueConstraint {
	uniques := make(map[string]UniqueConstraint)
	for _, field := range schema.Fields {
		if field.Unique {
			name := schema.namer.UniqueName(schema.Table, field.DBName)
			uniques[name] = UniqueConstraint{Name: name, Field: field}
		}
	}
	return uniques