1. 实现配置文件解析

2. 实现数据库连接

vendor/gorm.io/gorm/clause/from.go

@@ -0,0 +1,37 @@
+package clause
+
+// From from clause
+type From struct {
+	Tables []Table
+	Joins  []Join
+}
+
+// Name from clause name
+func (from From) Name() string {
+	return "FROM"
+}
+
+// Build build from clause
+func (from From) Build(builder Builder) {
+	if len(from.Tables) > 0 {
+		for idx, table := range from.Tables {
+			if idx > 0 {
+				builder.WriteByte(',')
+			}
+
+			builder.WriteQuoted(table)
+		}
+	} else {
+		builder.WriteQuoted(currentTable)
+	}
+
+	for _, join := range from.Joins {
+		builder.WriteByte(' ')
+		join.Build(builder)
+	}
+}
+
+// MergeClause merge from clause
+func (from From) MergeClause(clause *Clause) {
+	clause.Expression = from
+}