/// <summary>
/// 访问表示 null 合并运算的节点 a ?? b
/// </summary>
protected override Expression VisitCoalesce(BinaryExpression b)
{
// 例： a.Name ?? "TAN" => ISNULL(a.Name,'TAN')
_builder.Append("IFNULL(");
_visitor.Visit(b.Left is ConstantExpression ? b.Right : b.Left);
_builder.Append(',');
_visitor.Visit(b.Left is ConstantExpression ? b.Left : b.Right);
_builder.Append(')');
return(b);
}
/// <summary>
/// 访问 ToString 方法
/// </summary>
protected override Expression VisitToStringImpl(Expression node)
{
// => a.ID.ToString()
// 字符串不进行转换
if (node == null || node.Type == typeof(string))
{
return(_visitor.Visit(node));
}
ColumnAttribute column = null;
bool isUnicode = _provider.DbValue.IsUnicode(_visitedMark.Current, out column);
string native = isUnicode ? "NVARCHAR" : "VARCHAR";
// 其它类型转字符串
bool isDate = node.Type == typeof(DateTime) ||
node.Type == typeof(DateTime?) ||
node.Type == typeof(TimeSpan) ||
node.Type == typeof(TimeSpan?) ||
node.Type == typeof(DateTimeOffset) ||
node.Type == typeof(DateTimeOffset?);
if (isDate)
{
native = string.Format("{0}(64)", native);
_builder.Append("CONVERT(");
_builder.Append(native);
_builder.Append(",");
_visitor.Visit(node);
_builder.Append(",121)");
}
else if (node.Type == typeof(byte[]))
{
native = string.Format("{0}(max)", native);
_builder.Append("CONVERT(");
_builder.Append(native);
_builder.Append(",");
_visitor.Visit(node);
_builder.Append(",1)");
}
else if (node.Type == typeof(Guid))
{
native = string.Format("{0}(64)", native);
_builder.Append("CAST(");
_visitor.Visit(node);
_builder.Append(" AS ");
_builder.Append(native);
_builder.Append(')');
}
else
{
if (column != null && column.Size > 0)
{
native = string.Format("{0}({1})", native, column.Size);
}
else if (column != null && column.Size == -1)
{
native = string.Format("{0}(max)", native);
}
else
{
native = string.Format("{0}(max)", native);
}
_builder.Append("CAST(");
_visitor.Visit(node);
_builder.Append(" AS ");
_builder.Append(native);
_builder.Append(')');
}
return(node);
}
/// <summary>
/// 访问表示 null 合并运算的节点 a ?? b
/// </summary>
public override Expression VisitCoalesce(BinaryExpression b)
{
// 例： a.Name ?? "TAN" => ISNULL(a.Name,'TAN')
_builder.Append("COALESCE(");
_visitor.Visit(b.Left is ConstantExpression ? b.Right : b.Left);
_builder.Append(",");
_visitor.Visit(b.Left is ConstantExpression ? b.Left : b.Right);
_builder.Append(")");
return(b);
}
