From 6ecce561e6c8baf41e1fcea6d55238f3f4a46f4c Mon Sep 17 00:00:00 2001
From: Matt Schiros <matthews@unity3d.com>
Date: Thu, 17 Jan 2019 11:57:22 -0800
Subject: [PATCH] added arbitrary join conditions as a tag option for many2many
 relationships

---
 callback_query.go     | 2 +-
 join_table_handler.go | 6 +++++-
 model_struct.go       | 8 ++++++++
 3 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/callback_query.go b/callback_query.go
index 593e5d30..7facc42b 100644
--- a/callback_query.go
+++ b/callback_query.go
@@ -18,7 +18,7 @@ func queryCallback(scope *Scope) {
 	if _, skip := scope.InstanceGet("gorm:skip_query_callback"); skip {
 		return
 	}
-	
+
 	//we are only preloading relations, dont touch base model
 	if _, skip := scope.InstanceGet("gorm:only_preload"); skip {
 		return
diff --git a/join_table_handler.go b/join_table_handler.go
index a036d46d..d97f6d52 100644
--- a/join_table_handler.go
+++ b/join_table_handler.go
@@ -42,6 +42,7 @@ type JoinTableHandler struct {
 	TableName   string          `sql:"-"`
 	Source      JoinTableSource `sql:"-"`
 	Destination JoinTableSource `sql:"-"`
+	ArbitraryJoinConditions []string `sql:"-"`
 }
 
 // SourceForeignKeys return source foreign keys
@@ -66,7 +67,7 @@ func (s *JoinTableHandler) Setup(relationship *Relationship, tableName string, s
 			AssociationDBName: dbName,
 		})
 	}
-
+	
 	s.Destination = JoinTableSource{ModelType: destination}
 	s.Destination.ForeignKeys = []JoinTableForeignKey{}
 	for idx, dbName := range relationship.AssociationForeignFieldNames {
@@ -75,6 +76,8 @@ func (s *JoinTableHandler) Setup(relationship *Relationship, tableName string, s
 			AssociationDBName: dbName,
 		})
 	}
+
+	s.ArbitraryJoinConditions = relationship.ArbitraryJoinConditions
 }
 
 // Table return join table's table name
@@ -174,6 +177,7 @@ func (s JoinTableHandler) JoinWith(handler JoinTableHandlerInterface, db *DB, so
 		for _, foreignKey := range s.Destination.ForeignKeys {
 			joinConditions = append(joinConditions, fmt.Sprintf("%v.%v = %v.%v", quotedTableName, scope.Quote(foreignKey.DBName), destinationTableName, scope.Quote(foreignKey.AssociationDBName)))
 		}
+		joinConditions = append(joinConditions, s.ArbitraryJoinConditions...)
 
 		var foreignDBNames []string
 		var foreignFieldNames []string
diff --git a/model_struct.go b/model_struct.go
index 9e93db63..9d49b299 100644
--- a/model_struct.go
+++ b/model_struct.go
@@ -133,6 +133,7 @@ type Relationship struct {
 	AssociationForeignFieldNames []string
 	AssociationForeignDBNames    []string
 	JoinTableHandler             JoinTableHandlerInterface
+	ArbitraryJoinConditions      []string
 }
 
 func getForeignField(column string, fields []*StructField) *StructField {
@@ -339,6 +340,13 @@ func (scope *Scope) GetModelStruct() *ModelStruct {
 										}
 									}
 
+									// Check for arbitrary join conditions supplied in the tag
+
+									if arbitraryConditions,_ := field.TagSettingsGet("ARBITRARY_JOIN_CONDITIONS"); arbitraryConditions != "" {
+										relationship.ArbitraryJoinConditions = strings.Split(arbitraryConditions, ",")
+									}
+
+
 									joinTableHandler := JoinTableHandler{}
 									joinTableHandler.Setup(relationship, ToTableName(many2many), reflectType, elemType)
 									relationship.JoinTableHandler = &joinTableHandler