From cc07ee0444cac16388778b413be93e877ed80816 Mon Sep 17 00:00:00 2001
From: Jinzhu <wosmvp@gmail.com>
Date: Sat, 30 May 2020 12:46:30 +0800
Subject: [PATCH] Support mssql merge

---
 dialects/mssql/create.go | 143 +++++++++++++++++++++++++++++----------
 dialects/mssql/mssql.go  |   2 +-
 2 files changed, 108 insertions(+), 37 deletions(-)

diff --git a/dialects/mssql/create.go b/dialects/mssql/create.go
index 4aecce10..9183ba76 100644
--- a/dialects/mssql/create.go
+++ b/dialects/mssql/create.go
@@ -16,49 +16,48 @@ func Create(db *gorm.DB) {
 	}
 
 	if db.Statement.SQL.String() == "" {
-		db.Statement.AddClauseIfNotExists(clause.Insert{
-			Table: clause.Table{Name: db.Statement.Table},
-		})
-		db.Statement.AddClause(callbacks.ConvertToCreateValues(db.Statement))
+		c := db.Statement.Clauses["ON CONFLICT"]
+		onConflict, hasConflict := c.Expression.(clause.OnConflict)
 
-		db.Statement.Build("INSERT")
-		db.Statement.WriteByte(' ')
-
-		c := db.Statement.Clauses["VALUES"]
-		if values, ok := c.Expression.(clause.Values); ok {
-			if len(values.Columns) > 0 {
-				db.Statement.WriteByte('(')
-				for idx, column := range values.Columns {
-					if idx > 0 {
-						db.Statement.WriteByte(',')
-					}
-					db.Statement.WriteQuoted(column)
-				}
-				db.Statement.WriteByte(')')
-
-				if db.Statement.Schema.PrioritizedPrimaryField != nil {
-					db.Statement.WriteString(" OUTPUT INSERTED.")
-					db.Statement.WriteQuoted(db.Statement.Schema.PrioritizedPrimaryField.DBName)
-				}
-
-				db.Statement.WriteString(" VALUES ")
-
-				for idx, value := range values.Values {
-					if idx > 0 {
-						db.Statement.WriteByte(',')
-					}
+		if hasConflict {
+			MergeCreate(db, onConflict)
+		} else {
+			db.Statement.AddClauseIfNotExists(clause.Insert{Table: clause.Table{Name: db.Statement.Table}})
+			db.Statement.Build("INSERT")
+			db.Statement.WriteByte(' ')
 
+			db.Statement.AddClause(callbacks.ConvertToCreateValues(db.Statement))
+			if values, ok := db.Statement.Clauses["VALUES"].Expression.(clause.Values); ok {
+				if len(values.Columns) > 0 {
 					db.Statement.WriteByte('(')
-					db.Statement.AddVar(db.Statement, value...)
+					for idx, column := range values.Columns {
+						if idx > 0 {
+							db.Statement.WriteByte(',')
+						}
+						db.Statement.WriteQuoted(column)
+					}
 					db.Statement.WriteByte(')')
+
+					outputInserted(db)
+
+					db.Statement.WriteString(" VALUES ")
+
+					for idx, value := range values.Values {
+						if idx > 0 {
+							db.Statement.WriteByte(',')
+						}
+
+						db.Statement.WriteByte('(')
+						db.Statement.AddVar(db.Statement, value...)
+						db.Statement.WriteByte(')')
+					}
+
+					db.Statement.WriteString(";")
+				} else {
+					db.Statement.WriteString("DEFAULT VALUES")
 				}
-			} else {
-				db.Statement.WriteString("DEFAULT VALUES")
 			}
 		}
-
-		db.Statement.WriteByte(' ')
-		db.Statement.Build("ON CONFLICT")
 	}
 
 	rows, err := db.Statement.ConnPool.QueryContext(db.Statement.Context, db.Statement.SQL.String(), db.Statement.Vars...)
@@ -93,3 +92,75 @@ func Create(db *gorm.DB) {
 		db.AddError(err)
 	}
 }
+
+func MergeCreate(db *gorm.DB, onConflict clause.OnConflict) {
+	values := callbacks.ConvertToCreateValues(db.Statement)
+
+	db.Statement.WriteString("MERGE INTO ")
+	db.Statement.WriteQuoted(db.Statement.Table)
+	db.Statement.WriteString(" USING (VALUES")
+	for idx, value := range values.Values {
+		if idx > 0 {
+			db.Statement.WriteByte(',')
+		}
+
+		db.Statement.WriteByte('(')
+		db.Statement.AddVar(db.Statement, value...)
+		db.Statement.WriteByte(')')
+	}
+
+	db.Statement.WriteString(") AS source (")
+	for idx, column := range values.Columns {
+		if idx > 0 {
+			db.Statement.WriteByte(',')
+		}
+		db.Statement.WriteQuoted(column.Name)
+	}
+	db.Statement.WriteString(") ON ")
+
+	var where clause.Where
+	for _, field := range db.Statement.Schema.PrimaryFields {
+		where.Exprs = append(where.Exprs, clause.Eq{
+			Column: clause.Column{Table: db.Statement.Table, Name: field.DBName},
+			Value:  clause.Column{Table: "source", Name: field.DBName},
+		})
+	}
+	where.Build(db.Statement)
+
+	if len(onConflict.DoUpdates) > 0 {
+		db.Statement.WriteString(" WHEN MATCHED THEN UPDATE SET ")
+		onConflict.DoUpdates.Build(db.Statement)
+	}
+
+	db.Statement.WriteString(" WHEN NOT MATCHED THEN INSERT (")
+
+	for idx, column := range values.Columns {
+		if idx > 0 {
+			db.Statement.WriteByte(',')
+		}
+		db.Statement.WriteQuoted(column.Name)
+	}
+
+	db.Statement.WriteString(") VALUES (")
+
+	for idx, column := range values.Columns {
+		if idx > 0 {
+			db.Statement.WriteByte(',')
+		}
+		db.Statement.WriteQuoted(clause.Column{
+			Table: "source",
+			Name:  column.Name,
+		})
+	}
+
+	db.Statement.WriteString(")")
+	outputInserted(db)
+	db.Statement.WriteString(";")
+}
+
+func outputInserted(db *gorm.DB) {
+	if db.Statement.Schema.PrioritizedPrimaryField != nil {
+		db.Statement.WriteString(" OUTPUT INSERTED.")
+		db.Statement.WriteQuoted(db.Statement.Schema.PrioritizedPrimaryField.DBName)
+	}
+}
diff --git a/dialects/mssql/mssql.go b/dialects/mssql/mssql.go
index 35fcb484..de82f375 100644
--- a/dialects/mssql/mssql.go
+++ b/dialects/mssql/mssql.go
@@ -112,7 +112,7 @@ func (dialector Dialector) DataTypeOf(field *schema.Field) string {
 		if size > 0 && size <= 4000 {
 			return fmt.Sprintf("nvarchar(%d)", size)
 		}
-		return "ntext"
+		return "nvarchar(MAX)"
 	case schema.Time:
 		return "datetimeoffset"
 	case schema.Bytes: