add sample to show how to build JOIN with Struct

Author: huandu

README.md

@@ -52,7 +52,7 @@ fmt.Println(sql)
 // SELECT id, name FROM demo.user WHERE status = 1 LIMIT 10
 ```
 
-In the most cases, we need to escape all input from user. In this case, create a builder before starting.
+In the most common cases, we need to escape all input from user. In this case, create a builder before starting.
 
 ```go
 sb := sqlbuilder.NewSelectBuilder()
@@ -222,7 +222,7 @@ type ATable struct {
     Field1     string                                    // If a field doesn't has a tag, use "Field1" as column name in SQL.
     Field2     int    `db:"field2"`                      // Use "db" in field tag to set column name used in SQL.
     Field3     int64  `db:"field3" fieldtag:"foo,bar"`   // Set fieldtag to a field. We can call `WithTag` to include fields with tag or `WithoutTag` to exclude fields with tag.
-    Field4     int64  `db:"field4" fieldtag:"foo"`       // If we use `s.WithTag("foo").Select(table)`, columnes of SELECT are field3 and field4.
+    Field4     int64  `db:"field4" fieldtag:"foo"`       // If we use `s.WithTag("foo").Select("t")`, columnes of SELECT are "t.field3" and "t.field4".
     Field5     string `db:"field5" fieldas:"f5_alias"`   // Use "fieldas" in field tag to set a column alias (AS) used in SELECT.
     Ignored    int32  `db:"-"`                           // If we set field name as "-", Struct will ignore it.
     unexported int                                       // Unexported field is not visible to Struct.
@@ -232,6 +232,10 @@ type ATable struct {
     // The `omitempty` can be written as a function.
     // In this case, omit empty field `Tagged` when UPDATE for tag `tag1` and `tag3` but not `tag2`.
     Tagged     string `db:"tagged" fieldopt:"omitempty(tag1,tag3)" fieldtag:"tag1,tag2,tag3"`
+
+    // By default, the `SelectFrom("t")` will add the "t." to all names of fields matched tag.
+    // We can add dot to field name to disable this behavior.
+    FieldWithTableAlias string `db:"m.field"`
 }
 ```
 
@@ -254,7 +258,7 @@ var userStruct = NewStruct(new(User))
 
 func ExampleStruct() {
     // Prepare SELECT query.
-    //     SELECT id, name, status FROM user WHERE id = 1234
+    //     SELECT user.id, user.name, user.status FROM user WHERE id = 1234
     sb := userStruct.SelectFrom("user")
     sb.Where(sb.Equal("id", 1234))
 

struct.go

@@ -307,10 +307,11 @@ func (s *Struct) selectFromWithTags(table string, with, without []string) (sb *S
 
 	buf := newStringBuilder()
 	cols := make([]string, 0, len(tagged.ForRead))
+	tableAlias := parseTableAlias(table)
 
 	for _, sf := range tagged.ForRead {
 		if s.Flavor != CQL && !strings.ContainsRune(sf.Alias, '.') {
-			buf.WriteString(table)
+			buf.WriteString(tableAlias)
 			buf.WriteRune('.')
 		}
 		buf.WriteString(sf.NameForSelect(s.Flavor))
@@ -323,6 +324,16 @@ func (s *Struct) selectFromWithTags(table string, with, without []string) (sb *S
 	return sb
 }
 
+func parseTableAlias(table string) string {
+	idx := strings.LastIndex(table, " ")
+
+	if idx == -1 {
+		return table
+	}
+
+	return table[idx+1:]
+}
+
 // Update creates a new `UpdateBuilder` with table name.
 // By default, all exported fields of the s is assigned in UPDATE with the field values from value.
 // If value's type is not the same as that of s, Update returns a dummy `UpdateBuilder` with table name.

struct_test.go

@@ -386,6 +386,37 @@ func ExampleStruct_useStructAsORM() {
 	// sqlbuilder.User{ID:1234, Name:"huandu", Status:1}
 }
 
+func ExampleStruct_buildJOIN() {
+	// Suppose we're going to query a "member" table joined with "user" table.
+	type Member struct {
+		ID         string    `db:"id"`
+		UserID     string    `db:"user_id"`
+		MemberName int       `db:"name"`
+		CreatedAt  time.Time `db:"created_at"`
+
+		// Add "u." prefix to the field name to specify the field in "user" table.
+		Name  string `db:"u.name"`
+		Email string `db:"u.email"`
+	}
+
+	// Parse member struct. The memberStruct can be a global variable.
+	// It's guraanteed to be thread-safe.
+	var memberStruct = NewStruct(new(Member))
+
+	// Prepare JOIN query.
+	sb := memberStruct.SelectFrom("member m").Join("user u", "m.user_id = u.user_id")
+	sb.Where(sb.Like("m.name", "Huan%"))
+
+	sql, args := sb.Build()
+
+	fmt.Println(sql)
+	fmt.Println(args)
+
+	// Output:
+	// SELECT m.id, m.user_id, m.name, m.created_at, u.name, u.email FROM member m JOIN user u ON m.user_id = u.user_id WHERE m.name LIKE ?
+	// [Huan%]
+}
+
 var orderDB testDB = 1
 
 func ExampleStruct_WithTag() {