#486 - Postgres DDL - Add "if exists" to alter table [if exists] drop constraint if exists ....

src/main/java/com/avaje/ebean/dbmigration/ddlgeneration/platform/PlatformDdl.java

@@ -53,6 +53,8 @@ public class PlatformDdl {
 
   protected String identitySuffix = " auto_increment";
 
+  protected String alterTableIfExists = "";
+
   protected String dropConstraintIfExists = "drop constraint if exists";
 
   protected String dropIndexIfExists = "drop index if exists ";
@@ -150,7 +152,7 @@ public class PlatformDdl {
    * Return the drop foreign key clause.
    */
   public String alterTableDropForeignKey(String tableName, String fkName) {
-    return "alter table " + tableName + " " + dropConstraintIfExists + " " + fkName;
+    return "alter table " + alterTableIfExists + tableName + " " + dropConstraintIfExists + " " + fkName;
   }
 
   /**

src/main/java/com/avaje/ebean/dbmigration/ddlgeneration/platform/PostgresDdl.java

@@ -13,6 +13,7 @@ public class PostgresDdl extends PlatformDdl {
     this.historyDdl = new PostgresHistoryDdl();
     this.dropTableCascade = " cascade";
     this.columnSetType = "type ";
+    this.alterTableIfExists = "if exists ";
   }
 
   /**