Support loading association using Join query (#302)

* Add join assoc query builder

* support loading assoc using join

* fix select alias

join_query.go

@@ -20,15 +20,40 @@ func (jq JoinQuery) Build(query *Query) {
 	}
 }
 
-func (jq *JoinQuery) Populate(docMeta DocumentMeta) {
+func (jq *JoinQuery) Populate(query *Query, docMeta DocumentMeta) {
 	var (
 		assocMeta    = docMeta.Association(jq.Assoc)
 		assocDocMeta = assocMeta.DocumentMeta()
 	)
 
-	jq.Table = assocDocMeta.Table()
-	jq.To = jq.Table + "." + assocMeta.ForeignField()
+	jq.Table = assocDocMeta.Table() + " as " + jq.Assoc
+	jq.To = jq.Assoc + "." + assocMeta.ForeignField()
 	jq.From = docMeta.Table() + "." + assocMeta.ReferenceField()
+
+	// load association if defined and supported
+	if assocMeta.Type() == HasOne || assocMeta.Type() == BelongsTo {
+		var (
+			load        = false
+			selectField = jq.Assoc + ".*"
+		)
+
+		for i := range query.SelectQuery.Fields {
+			if load && i > 0 {
+				query.SelectQuery.Fields[i-1] = query.SelectQuery.Fields[i]
+			}
+			if query.SelectQuery.Fields[i] == selectField {
+				load = true
+			}
+		}
+
+		if load {
+			fields := make([]string, len(assocDocMeta.Fields()))
+			for i, f := range assocDocMeta.Fields() {
+				fields[i] = jq.Assoc + "." + f + " as " + jq.Assoc + "." + f
+			}
+			query.SelectQuery.Fields = append(query.SelectQuery.Fields[:(len(query.SelectQuery.Fields)-1)], fields...)
+		}
+	}
 }
 
 // NewJoinWith query with custom join mode, table, field and additional filters with AND condition.

join_query_test.go

@@ -73,34 +73,49 @@ func TestJoin(t *testing.T) {
 
 func TestJoinAssoc_hasOne(t *testing.T) {
 	var (
-		populated = rel.Build("", rel.NewJoinAssoc("address")).
-			Populate(rel.NewDocument(&rel.User{}, false).Meta()).
-			JoinQuery[0]
+		populated = rel.Build("", rel.Select("*", "address.*"), rel.NewJoinAssoc("address")).
+			Populate(rel.NewDocument(&rel.User{}, false).Meta())
 	)
 
 	assert.Equal(t, rel.JoinQuery{
 		Mode:  "JOIN",
-		Table: "user_addresses",
-		To:    "user_addresses.user_id",
+		Table: "user_addresses as address",
+		To:    "address.user_id",
 		From:  "users.id",
 		Assoc: "address",
-	}, populated)
+	}, populated.JoinQuery[0])
+	assert.Equal(t, []string{
+		"*",
+		"address.id as address.id",
+		"address.user_id as address.user_id",
+		"address.street as address.street",
+		"address.notes as address.notes",
+		"address.deleted_at as address.deleted_at",
+	}, populated.SelectQuery.Fields)
 }
 
 func TestJoinPopulate_hasOnePtr(t *testing.T) {
 	var (
-		populated = rel.Build("", rel.NewJoinAssoc("work_address")).
-			Populate(rel.NewDocument(&rel.User{}, false).Meta()).
-			JoinQuery[0]
+		populated = rel.Build("", rel.Select("id", "work_address.*", "name"), rel.NewJoinAssoc("work_address")).
+			Populate(rel.NewDocument(&rel.User{}, false).Meta())
 	)
 
 	assert.Equal(t, rel.JoinQuery{
 		Mode:  "JOIN",
-		Table: "user_addresses",
-		To:    "user_addresses.user_id",
+		Table: "user_addresses as work_address",
+		To:    "work_address.user_id",
 		From:  "users.id",
 		Assoc: "work_address",
-	}, populated)
+	}, populated.JoinQuery[0])
+	assert.Equal(t, []string{
+		"id",
+		"name",
+		"work_address.id as work_address.id",
+		"work_address.user_id as work_address.user_id",
+		"work_address.street as work_address.street",
+		"work_address.notes as work_address.notes",
+		"work_address.deleted_at as work_address.deleted_at",
+	}, populated.SelectQuery.Fields)
 }
 
 func TestJoinPopulate_hasMany(t *testing.T) {
@@ -112,7 +127,7 @@ func TestJoinPopulate_hasMany(t *testing.T) {
 
 	assert.Equal(t, rel.JoinQuery{
 		Mode:  "JOIN",
-		Table: "transactions",
+		Table: "transactions as transactions",
 		To:    "transactions.user_id",
 		From:  "users.id",
 		Assoc: "transactions",
@@ -128,8 +143,8 @@ func TestJoinAssoc_belongsTo(t *testing.T) {
 
 	assert.Equal(t, rel.JoinQuery{
 		Mode:  "JOIN",
-		Table: "users",
-		To:    "users.id",
+		Table: "users as user",
+		To:    "user.id",
 		From:  "user_addresses.user_id",
 		Assoc: "user",
 	}, populated)

query.go

@@ -11,7 +11,7 @@ type Querier interface {
 }
 
 type QueryPopulator interface {
-	Populate(DocumentMeta)
+	Populate(*Query, DocumentMeta)
 }
 
 // Build for given table using given queriers.
@@ -130,7 +130,7 @@ func (q Query) Build(query *Query) {
 
 func (q Query) Populate(documentMeta DocumentMeta) Query {
 	for i := range q.queryPopulators {
-		q.queryPopulators[i].Populate(documentMeta)
+		q.queryPopulators[i].Populate(&q, documentMeta)
 	}
 
 	return q

query_test.go

@@ -383,7 +383,7 @@ func TestQuery_JoinAssoc(t *testing.T) {
 		JoinQuery: []rel.JoinQuery{
 			{
 				Mode:  "JOIN",
-				Table: "transactions",
+				Table: "transactions as transactions",
 				To:    "transactions.user_id",
 				From:  "users.id",
 				Assoc: "transactions",