From 400d51c9279d741c1df9301315b73271f6ffeb82 Mon Sep 17 00:00:00 2001
From: Tri Dao <minhtri1396@gmail.com>
Date: Tue, 12 Nov 2024 12:23:58 +0700
Subject: [PATCH] feat(expression): support case-when expression

---
 clause/expr_case.go      | 54 ++++++++++++++++++++++++++++++++++++
 clause/expr_case_test.go | 60 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 114 insertions(+)
 create mode 100644 clause/expr_case.go
 create mode 100644 clause/expr_case_test.go

diff --git a/clause/expr_case.go b/clause/expr_case.go
new file mode 100644
index 000000000..bdcce9ab6
--- /dev/null
+++ b/clause/expr_case.go
@@ -0,0 +1,54 @@
+package clause
+
+type ExprCaseCondition struct {
+	When string
+	Then string
+	Vars []any
+}
+
+type ExprCaseElse struct {
+	Then string
+	Vars []any
+}
+
+type ExprCase struct {
+	Cases []*ExprCaseCondition
+	Else  *ExprCaseElse
+}
+
+func (expr ExprCase) Name() string {
+	return "CASE"
+}
+
+func (expr ExprCase) Build(builder Builder) {
+	var vars []any
+	for idx, condition := range expr.Cases {
+		if idx > 0 {
+			_ = builder.WriteByte(' ')
+		}
+		_, _ = builder.WriteString("WHEN ")
+		_, _ = builder.WriteString(condition.When)
+		_, _ = builder.WriteString(" THEN ")
+		_, _ = builder.WriteString(condition.Then)
+		if len(condition.Vars) > 0 {
+			vars = append(vars, condition.Vars...)
+		}
+	}
+
+	if expr.Else != nil {
+		elseExpr := expr.Else
+		_, _ = builder.WriteString(" ELSE ")
+		_, _ = builder.WriteString(elseExpr.Then)
+		if len(elseExpr.Vars) > 0 {
+			vars = append(vars, elseExpr.Vars...)
+		}
+	}
+	_, _ = builder.WriteString(" END")
+
+	clauseExpr := Expr{SQL: "", Vars: vars}
+	clauseExpr.Build(builder)
+}
+
+func (expr ExprCase) MergeClause(clause *Clause) {
+	clause.Expression = expr
+}
diff --git a/clause/expr_case_test.go b/clause/expr_case_test.go
new file mode 100644
index 000000000..c06d09e2e
--- /dev/null
+++ b/clause/expr_case_test.go
@@ -0,0 +1,60 @@
+package clause_test
+
+import (
+	"testing"
+
+	"gorm.io/gorm"
+	"gorm.io/gorm/clause"
+)
+
+func Test_ExprCase(t *testing.T) {
+	type exampleUser struct {
+		ID   string
+		Name string
+	}
+
+	inputUsers := []*exampleUser{
+		{
+			ID:   "user-001",
+			Name: "user-name-001",
+		},
+		{
+			ID:   "user-002",
+			Name: "user-name-002",
+		},
+	}
+
+	userIDs := make([]string, len(inputUsers))
+	userNameCases := make([]*clause.ExprCaseCondition, len(inputUsers))
+	for idx, user := range inputUsers {
+		userIDs[idx] = user.ID
+		userNameCases[idx] = &clause.ExprCaseCondition{
+			When: "user_id=?",
+			Then: "?",
+			Vars: []any{
+				user.ID,
+				user.Name,
+			},
+		}
+	}
+
+	sqlQuery := db.ToSQL(func(db *gorm.DB) *gorm.DB {
+		return db.
+			Table("users").
+			Where("user_id IN (?)", userIDs).
+			UpdateColumns(map[string]any{
+				"user_name": clause.ExprCase{
+					Cases: userNameCases,
+					Else: &clause.ExprCaseElse{
+						Then: "user_name",
+						Vars: nil,
+					},
+				},
+			})
+	})
+
+	expectedSQLQuery := "UPDATE `users` SET `user_name`=CASE WHEN user_id=\"user-001\" THEN \"user-name-001\" WHEN user_id=\"user-002\" THEN \"user-name-002\" ELSE user_name END WHERE user_id IN (\"user-001\",\"user-002\")"
+	if sqlQuery != expectedSQLQuery {
+		t.Errorf("SQLQuery is mismatch actual: %v expected:%v\n", sqlQuery, expectedSQLQuery)
+	}
+}