Add function to check if db error is a check constraint violation (#142)

internal/db/error.go

@@ -58,3 +58,20 @@ func IsUniqueError(err error) bool {
 
 	return false
 }
+
+// IsCheckConstraintError returns a boolean indicating whether the error is
+// known to report a check constraint violation.
+func IsCheckConstraintError(err error) bool {
+	if err == nil {
+		return false
+	}
+
+	var pqError *pq.Error
+	if errors.As(err, &pqError) {
+		if pqError.Code.Name() == "check_violation" {
+			return true
+		}
+	}
+
+	return false
+}

internal/db/error_test.go

@@ -43,3 +43,40 @@ func TestError_IsUnique(t *testing.T) {
 		})
 	}
 }
+
+func TestError_IsCheckConstraint(t *testing.T) {
+	var tests = []struct {
+		name string
+		in   error
+		want bool
+	}{
+		{
+			name: "nil-error",
+			in:   nil,
+			want: false,
+		},
+		{
+			name: "postgres-not-check-constraint",
+			in: &pq.Error{
+				Code: pq.ErrorCode("23505"),
+			},
+			want: false,
+		},
+		{
+			name: "postgres-is-check-constraint",
+			in: &pq.Error{
+				Code: pq.ErrorCode("23514"),
+			},
+			want: true,
+		},
+	}
+	for _, tt := range tests {
+		tt := tt
+		t.Run(tt.name, func(t *testing.T) {
+			assert := assert.New(t)
+			err := tt.in
+			got := IsCheckConstraintError(err)
+			assert.Equal(tt.want, got)
+		})
+	}
+}