我尝试使用ServiceStack Ormlite编写以下LINQ查询。
dbConn.Select<Product>(p => p.IsActive.HasValue && p.IsActive.Value)
在这里,产品是我的项目类,&#34; IsActive&#34;是该类中的Nullable Bool属性。当该行执行时,它总是抛出&#34; InvalidOperationException&#34;消息
变量&#39; p&#39;类型&#39;&#39;引用范围&#39;&#39;,但未定义
我尝试了以下不同的变体,但仍有相同的异常结果
dbConn.Select<Product>(p => p.IsActive.HasValue == true && p.IsActive.Value == true)
dbConn.Select<Product>(p => p.IsActive != null && p.IsActive.Value == true)
但如果我只是写
dbConn.Select<Product>(p => p.IsActive.HasValue)
然后它有效。
我很困惑,问题是什么?这是servicestack ormlite问题吗?答案 0 :(得分:2)
我的回答可以使用servicestack ormlite处理Nullable值,例如“value”和“HasValue”。而且还有datetime可空,比如'createdate.value.Year'。 你必须改变两个的地方。
protected virtual object VisitMemberAccess(MemberExpression m)
{
if (m.Expression != null)
{
if (m.Member.DeclaringType.IsNullableType())
{
if (m.Member.Name == nameof(Nullable<bool>.Value))
return Visit(m.Expression);
if (m.Member.Name == nameof(Nullable<bool>.HasValue))
{
var doesNotEqualNull = Expression.NotEqual(m.Expression, Expression.Constant(null));
return Visit(doesNotEqualNull); // Nullable<T>.HasValue is equivalent to "!= null"
}
throw new ArgumentException(string.Format("Expression '{0}' accesses unsupported property '{1}' of Nullable<T>", m, m.Member));
}
if (m.Member.DeclaringType == typeof(DateTime))
{
var ExpressionInfo = m.Expression as MemberExpression;
if (ExpressionInfo.Member.DeclaringType.IsNullableType())
{
if (ExpressionInfo.Member.Name == nameof(Nullable<bool>.Value))
{
var modelType = (ExpressionInfo.Expression as MemberExpression).Expression.Type;
var tableDef = modelType.GetModelDefinition();
var columnName = (ExpressionInfo.Expression as MemberExpression).Member.Name;
var QuotedColumnName = GetQuotedColumnName(tableDef, columnName);
if (m.Member.Name == "Year")
{
return new PartialSqlString(string.Format("DATEPART(yyyy,{0})", QuotedColumnName));
}
if (m.Member.Name == "Month")
return new PartialSqlString(string.Format("DATEPART(mm,{0})", QuotedColumnName));
}
if (ExpressionInfo.Member.Name == nameof(Nullable<bool>.HasValue))
{
var doesNotEqualNull = Expression.NotEqual(ExpressionInfo.Expression, Expression.Constant(null));
return Visit(doesNotEqualNull); // Nullable<T>.HasValue is equivalent to "!= null"
}
}
else
{
var modelType = ExpressionInfo.Expression.Type;
var tableDef = modelType.GetModelDefinition();
var columnName = ExpressionInfo.Member.Name;
var QuotedColumnName = GetQuotedColumnName(tableDef, columnName);
if (m.Member.Name == "Year")
return new PartialSqlString(string.Format("DATEPART(yyyy,{0})", QuotedColumnName));
if (m.Member.Name == "Month")
return new PartialSqlString(string.Format("DATEPART(mm,{0})", QuotedColumnName));
}
}
if (m.Expression.NodeType == ExpressionType.Parameter || m.Expression.NodeType == ExpressionType.Convert)
{
var propertyInfo = (PropertyInfo)m.Member;
var modelType = m.Expression.Type;
if (m.Expression.NodeType == ExpressionType.Convert)
{
var unaryExpr = m.Expression as UnaryExpression;
if (unaryExpr != null)
{
modelType = unaryExpr.Operand.Type;
}
}
var tableDef = modelType.GetModelDefinition();
if (propertyInfo.PropertyType.IsEnum)
return new EnumMemberAccess(
GetQuotedColumnName(tableDef, m.Member.Name), propertyInfo.PropertyType);
return new PartialSqlString(GetQuotedColumnName(tableDef, m.Member.Name));
}
}
var member = Expression.Convert(m, typeof(object));
var lambda = Expression.Lambda<Func<object>>(member);
var getter = lambda.Compile();
return getter();
}
protected virtual object VisitLambda(LambdaExpression lambda)
{
if (lambda.Body.NodeType == ExpressionType.MemberAccess && sep == " ")
{
MemberExpression m = lambda.Body as MemberExpression;
if (m.Expression != null)
{
string r = VisitMemberAccess(m).ToString();
if (m.Member.DeclaringType.IsNullableType())
return r;
return string.Format("{0}={1}", r, GetQuotedTrueValue());
}
}
return Visit(lambda.Body);
}
答案 1 :(得分:1)
这是Linq的本质。为了达到你所需要的,你需要使用两个关闭的地方:
public void CreateSaveFile(string fileName, TreeView treeView)
{
using (StreamWriter streamWriter = new StreamWriter(fileName))
{
// Print each node recursively.
TreeNodeCollection nodes = treeView.Nodes;
foreach (TreeNode n in nodes)
{
WriteRecursive(streamWriter, n);
}
streamWriter.Close(); // Optional since we have "using", but good practice to include.
}
}