LINQ独立项
我有一个包含约会的数据库。可以同时安排多个约会。我想检索一个不包括重复时间的可用约会时间列表 编辑 例如,我的数据库中可能有LINQ独立项,linq,Linq,我有一个包含约会的数据库。可以同时安排多个约会。我想检索一个不包括重复时间的可用约会时间列表 编辑 例如,我的数据库中可能有 REQUEST_ID REQUESTER_ID APPOINTMENT_TIME 1 0 30-JUN-13 03.30.00 AM 2 1 30-JUN-13 03.30.00 AM 3 0 30-JUN-13 03.
REQUEST_ID REQUESTER_ID APPOINTMENT_TIME
1 0 30-JUN-13 03.30.00 AM
2 1 30-JUN-13 03.30.00 AM
3 0 30-JUN-13 03.30.00 AM
4 0 30-JUN-13 03.30.00 AM
5 3 30-JUN-13 03.35.00 AM
6 0 30-JUN-13 03.45.00 AM
7 0 30-JUN-13 03.45.00 AM
我想退货
REQUEST_ID REQUESTER_ID APPOINTMENT_TIME
1 0 30-JUN-13 03.30.00 AM
6 0 30-JUN-13 03.45.00 AM
结束编辑
此查询返回所有可用的约会时段
var data =
(from a in db.FLU_SHOT
where a.REQUESTER_ID == 0
select a).ToArray();
此查询只返回次,我将丢失数据库中的其余信息
var times =
(from a in data
orderby Convert.ToDateTime(a.APPOINTMENT_TIME)
select a.APPOINTMENT_TIME).Distinct().ToArray();
此查询返回与第一个查询相同的信息
var times =
(from a in data
orderby Convert.ToDateTime(a.APPOINTMENT_TIME)
select a).Distinct().ToArray();
任何帮助都将不胜感激。您正在寻找的区别于
:
var times =
(from a in data
orderby Convert.ToDateTime(a.APPOINTMENT_TIME)
select a).DistinctBy(a => a.APPOINTMENT_TIME).ToArray();
var times = data.GroupBy(d => Convert.ToDateTime(d.APPOINTMENT_TIME))
.Select(g => g.First())
.ToArray();
或者,您可以使用基本的GroupBy
方法:
var times =
(from a in data
orderby Convert.ToDateTime(a.APPOINTMENT_TIME)
select a).GroupBy(a => a.APPOINTMENT_TIME).Select(g => g.First()).ToArray();
或者我的自定义lambda相等比较器(这比GroupBy
快,但比DistinctBy
慢,正如Servy多次指出的那样):
下面是它的代码:
public class PropertyEqualityComparer<TObject, TProperty>
: IEqualityComparer<TObject>
{
Func<TObject, TProperty> _selector;
IEqualityComparer<TProperty> _internalComparer;
public PropertyEqualityComparer(Func<TObject, TProperty> propertySelector,
IEqualityComparer<TProperty> innerEqualityComparer = null)
{
_selector = propertySelector;
_internalComparer = innerEqualityComparer;
}
public int GetHashCode(TObject obj)
{
return _selector(obj).GetHashCode();
}
public bool Equals(TObject x, TObject y)
{
IEqualityComparer<TProperty> comparer =
_internalComparer ?? EqualityComparer<TProperty>.Default;
return comparer.Equals(_selector(x), _selector(y));
}
}
//and here's a class to help instantiate it with anonymous objects
public static class PropertyEqualityComparer
{
public static PropertyEqualityComparer<TObject, TProperty>
GetNew<TObject, TProperty>(Func<TObject, TProperty> propertySelector)
{
return new PropertyEqualityComparer<TObject, TProperty>
(propertySelector);
}
public static PropertyEqualityComparer<TObject, TProperty>
GetNew<TObject, TProperty>
(Func<TObject, TProperty> propertySelector,
IEqualityComparer<TProperty> comparer)
{
return new PropertyEqualityComparer<TObject, TProperty>
(propertySelector, comparer);
}
}
公共类PropertyQualityComparer
:IEqualityComparer
{
函数选择器;
IEqualityComparer\u内部比较器;
公共财产资格比较人(Func Property Selector,
IEqualityComparer innerEqualityComparer=null)
{
_选择器=属性选择器;
_internalComparer=innerEqualityComparer;
}
公共int GetHashCode(TObject obj)
{
返回_选择器(obj).GetHashCode();
}
公共布尔等于(TObject x,TObject y)
{
IEqualityComparer比较器=
_internalComparer??EqualityComparer.Default;
返回比较器.Equals(_选择器(x),_选择器(y));
}
}
//这里有一个类可以帮助用匿名对象实例化它
公共静态类PropertyQualityComparer
{
公共静态属性质量比较程序
GetNew(函数属性选择器)
{
返回新属性EqualityComparer
(属性选择器);
}
公共静态属性质量比较程序
GetNew
(Func属性选择器,
IEqualityComparer(比较器)
{
返回新属性EqualityComparer
(属性选择器、比较器);
}
}
您要查找的不同于
:
var times =
(from a in data
orderby Convert.ToDateTime(a.APPOINTMENT_TIME)
select a).DistinctBy(a => a.APPOINTMENT_TIME).ToArray();
var times = data.GroupBy(d => Convert.ToDateTime(d.APPOINTMENT_TIME))
.Select(g => g.First())
.ToArray();
或者,您可以使用基本的GroupBy
方法:
var times =
(from a in data
orderby Convert.ToDateTime(a.APPOINTMENT_TIME)
select a).GroupBy(a => a.APPOINTMENT_TIME).Select(g => g.First()).ToArray();
或者我的自定义lambda相等比较器(这比GroupBy
快,但比DistinctBy
慢,正如Servy多次指出的那样):
下面是它的代码:
public class PropertyEqualityComparer<TObject, TProperty>
: IEqualityComparer<TObject>
{
Func<TObject, TProperty> _selector;
IEqualityComparer<TProperty> _internalComparer;
public PropertyEqualityComparer(Func<TObject, TProperty> propertySelector,
IEqualityComparer<TProperty> innerEqualityComparer = null)
{
_selector = propertySelector;
_internalComparer = innerEqualityComparer;
}
public int GetHashCode(TObject obj)
{
return _selector(obj).GetHashCode();
}
public bool Equals(TObject x, TObject y)
{
IEqualityComparer<TProperty> comparer =
_internalComparer ?? EqualityComparer<TProperty>.Default;
return comparer.Equals(_selector(x), _selector(y));
}
}
//and here's a class to help instantiate it with anonymous objects
public static class PropertyEqualityComparer
{
public static PropertyEqualityComparer<TObject, TProperty>
GetNew<TObject, TProperty>(Func<TObject, TProperty> propertySelector)
{
return new PropertyEqualityComparer<TObject, TProperty>
(propertySelector);
}
public static PropertyEqualityComparer<TObject, TProperty>
GetNew<TObject, TProperty>
(Func<TObject, TProperty> propertySelector,
IEqualityComparer<TProperty> comparer)
{
return new PropertyEqualityComparer<TObject, TProperty>
(propertySelector, comparer);
}
}
公共类PropertyQualityComparer
:IEqualityComparer
{
函数选择器;
IEqualityComparer\u内部比较器;
公共财产资格比较人(Func Property Selector,
IEqualityComparer innerEqualityComparer=null)
{
_选择器=属性选择器;
_internalComparer=innerEqualityComparer;
}
公共int GetHashCode(TObject obj)
{
返回_选择器(obj).GetHashCode();
}
公共布尔等于(TObject x,TObject y)
{
IEqualityComparer比较器=
_internalComparer??EqualityComparer.Default;
返回比较器.Equals(_选择器(x),_选择器(y));
}
}
//这里有一个类可以帮助用匿名对象实例化它
公共静态类PropertyQualityComparer
{
公共静态属性质量比较程序
GetNew(函数属性选择器)
{
返回新属性EqualityComparer
(属性选择器);
}
公共静态属性质量比较程序
GetNew
(Func属性选择器,
IEqualityComparer(比较器)
{
返回新属性EqualityComparer
(属性选择器、比较器);
}
}
每当我试图用LINQ(最终查询数据库)完成某件事情,而答案并不明显时,我首先编写SQL语句,然后找出如何将其转换为LINQ
如果您不知道如何进行翻译,那么您可以在线找到一个工具来提供帮助,或者您可以将查询转换为存储的proc或UDF,并从数据上下文调用它
在中等到高度复杂的查询中,手工编写几乎总是更好的。最有可能的是,LINQ吐出的任何东西都不会针对您的特定场景进行优化。通常,您可以诱使LINQ输出您想要的查询,但到那时,您已经浪费了大量宝贵的时间,而这些时间本可以花在其他更有效率的事情上
编辑:
为了更直接地回答你的问题,看起来你主要对约会时间感兴趣。在这种情况下,对该列进行分组,然后您可以循环遍历每个组并获得时间。每当我试图使用LINQ(最终查询数据库)完成某项任务,并且答案不明显时,我首先编写SQL语句,然后找出如何将其转换为LINQ 如果您不知道如何进行翻译,那么您可以在线找到一个工具来提供帮助,或者您可以将查询转换为存储的proc或UDF,并从数据上下文调用它 在中等到高度复杂的查询中,手工编写几乎总是更好的。最有可能的是,LINQ吐出的任何东西都不会针对您的特定场景进行优化。通常,您可以诱使LINQ输出您想要的查询,但到那时,您已经浪费了大量宝贵的时间,而这些时间本可以花在其他更有效率的事情上 编辑:
为了更直接地回答你的问题,看起来你主要对约会时间感兴趣。在这种情况下,对该列执行分组,然后您可以循环遍历每个组并获取时间。您可以使用
GroupBy
:
var times =
(from a in data
orderby Convert.ToDateTime(a.APPOINTMENT_TIME)
select a).DistinctBy(a => a.APPOINTMENT_TIME).ToArray();
var times = data.GroupBy(d => Convert.ToDateTime(d.APPOINTMENT_TIME))
.Select(g => g.First())
.ToArray();
您可以使用
GroupBy
:
var times =
(from a in data
orderby Convert.ToDateTime(a.APPOINTMENT_TIME)
select a).DistinctBy(a => a.APPOINTMENT_TIME).ToArray();
var times = data.GroupBy(d => Convert.ToDateTime(d.APPOINTMENT_TIME))
.Select(g => g.First())
.ToArray();
您的第一个、第二个和第三个查询差异很大。第二个和第三个查询在第一个查询之后运行,试图进一步细分数据。我正在分享我的尝试。您的第一个、第二个和第三个查询差异很大。第二个和第三个运行