Handle unimplemented/unsupported cases.

Author: fredericDelaporte

src/NHibernate/Dialect/Dialect.cs

@@ -526,8 +526,16 @@ public virtual string ForUpdateString
 			get { return " for update"; }
 		}
 
-		/// <summary> Is <tt>FOR UPDATE OF</tt> syntax supported? </summary>
-		/// <value> True if the database supports <tt>FOR UPDATE OF</tt> syntax; false otherwise. </value>
+		/// <summary>Is <c>FOR UPDATE OF</c> syntax supported?</summary>
+		/// <value><see langword="true"/> if the database supports <c>FOR UPDATE OF</c> syntax; <see langword="false"/> otherwise. </value>
+		public virtual bool ForUpdateOf
+			// By default, just check ForUpdateOfColumns. ForUpdateOf needs to be overriden only for dialect suppoting
+			// "For Update Of" on table aliases.
+			=> ForUpdateOfColumns;
+
+		/// <summary>Is <c>FOR UPDATE OF</c> syntax expecting columns?</summary>
+		/// <value><see langword="true"/> if the database expects a column list with <c>FOR UPDATE OF</c> syntax,
+		/// <see langword="false"/> if it expects table alias instead or do not support <c>FOR UPDATE OF</c> syntax.</value>
 		public virtual bool ForUpdateOfColumns
 		{
 			// by default we report no support

src/NHibernate/Dialect/InformixDialect.cs

@@ -175,8 +175,7 @@ public override string AddColumnString
 		//    throw new NotSupportedException();
 		//}
 
-		/// <summary> Is <tt>FOR UPDATE OF</tt> syntax supported? </summary>
-		/// <value> True if the database supports <tt>FOR UPDATE OF</tt> syntax; false otherwise. </value>
+		/// <inheritdoc />
 		public override bool ForUpdateOfColumns
 		{
 			get { return true; }

src/NHibernate/Dialect/PostgreSQLDialect.cs

@@ -227,6 +227,12 @@ public override SqlString GetLimitString(SqlString queryString, SqlString offset
 			return pagingBuilder.ToSqlString();
 		}
 
+		/// <inheritdoc />
+		public override bool ForUpdateOf => true;
+
+		/// <inheritdoc />
+		public override bool SupportsOuterJoinForUpdate => false;
+
 		public override string GetForUpdateString(string aliases)
 		{
 			return ForUpdateString + " of " + aliases;
@@ -318,7 +324,6 @@ public override string CurrentTimestampSelectString
 
 		public override bool SupportsUnboundedLobLocatorMaterialization => false;
 
-		public override bool SupportsOuterJoinForUpdate => false;
 		#endregion
 
 		[Serializable]

src/NHibernate/SqlCommand/SqlSelectBuilder.cs

@@ -305,11 +305,31 @@ private string GetForUpdateString()
 		{
 			if (!Dialect.SupportsOuterJoinForUpdate && HasOuterJoin())
 			{
-				if (Equals(lockMode, LockMode.Upgrade))
-					return Dialect.GetForUpdateString(mainTableAlias);
-				
-				if (Equals(lockMode, LockMode.UpgradeNoWait))
-					return Dialect.GetForUpdateNowaitString(mainTableAlias);
+				var isUpgrade = Equals(lockMode, LockMode.Upgrade);
+				var isUpgradeNoWait = !isUpgrade && (
+					Equals(lockMode, LockMode.UpgradeNoWait) || Equals(lockMode, LockMode.Force));
+				if (!isUpgrade && !isUpgradeNoWait)
+					return string.Empty;
+
+				if (!Dialect.ForUpdateOf)
+				{
+					log.Warn(
+						"Unsupported 'for update' case: 'for update' query with an outer join using a dialect not" +
+						"supporting it and not supporting 'for update of' clause. Discarding 'for" +
+						"update' clause.");
+					return string.Empty;
+				}
+
+				if (Dialect.ForUpdateOfColumns)
+				{
+					log.Warn(
+						"Unimplemented 'for update' case: 'for update' query with an outer join using a dialect not" +
+						"supporting it and requiring columns for its 'for update of' syntax. Discarding 'for" +
+						"update' clause.");
+					return string.Empty;
+				}
+
+				return isUpgrade ? Dialect.GetForUpdateString(mainTableAlias) : Dialect.GetForUpdateNowaitString(mainTableAlias);
 			}
 
 			return Dialect.GetForUpdateString(lockMode);