public override T Accept <T>(DbExpressionVisitor <T> visitor)
{
return(visitor.Visit(this));
}
/// <summary>
/// 访问表示 null 合并运算的节点 a ?? b
/// </summary>
/// <param name="b">二元表达式节点</param>
/// <returns></returns>
protected override Expression VisitCoalesce(BinaryExpression b)
{
// 例： a.Name ?? "TAN" => ISNULL(a.Name,'TAN')
Expression left = b.Left.NodeType == ExpressionType.Constant ? b.Right : b.Left;
Expression right = b.Left.NodeType == ExpressionType.Constant ? b.Left : b.Right;
_builder.Append("NVL(");
_visitor.Visit(left);
_builder.Append(",");
_visitor.Visit(right);
_builder.Append(')');
return(b);
}
public Expression VisitProjection(ProjectionExpression proj)
{
return(_defaultVisitor.Visit(proj));
}
/// <summary>
/// 访问表示 null 合并运算的节点 a ?? b
/// </summary>
/// <param name="b">二元表达式节点</param>
protected 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);
}
/// <summary>
/// 访问 StartWidth 方法
/// </summary>
/// <param name="m">方法表达式</param>
protected override Expression VisitStartsWith(MethodCallExpression m)
{
_visitor.Visit(m.Object);
if (this.NotOperands != null && this.NotOperands.Contains(m))
{
_builder.Append(" NOT");
}
_builder.Append(" LIKE ");
if (m.Arguments[0].CanEvaluate())
{
ColumnAttribute column = null;
bool unicode = SqlServerUtils.IsUnicode(_visitedMark.Current, out column);
string value = _constor.GetSqlValue(m.Arguments[0].Evaluate().Value, _builder.TranslateContext, column);
if (!_builder.Parameterized && value != null)
{
value = value.TrimStart('N').Trim('\'');
}
if (_builder.Parameterized)
{
_builder.Append("(");
_builder.Append(value);
_builder.Append(" + '%')");
}
else
{
if (unicode)
{
_builder.Append('N');
}
_builder.Append("'");
_builder.Append(value);
_builder.Append("%'");
}
}
else
{
_builder.Append("(");
_visitor.Visit(m.Arguments[0]);
_builder.Append(" + '%')");
}
return(m);
}