Linq将String比较为Double [英] Linq Compare String to Double

问题描述

如何创建一个LINQ查询，该查询接受一个字符串值列表（包含数字）并检查 maxLon （一个Double变量）



示例：

How to create a LINQ query that takes a list of string values (that has numbers) and check it against a maxLon (a Double variable)

Example:

Locquery = (DataServiceQuery<ava_location>)(from c in ctx.ava_locationSet 
                                            where (Double.Parse(c.fn_Longitude) <= maxLon)
                                            Select new ava_location
                                            {
                                               fn_Latitude = c.fn_Latitude,
                                               fn_Longitude = c.fn_Longitude,
                                            }).Skip(0).Take(MaxRows);

这个编译，但在执行时，我得到以下异常：

This compiles, but upon execution, I got the following exception:

System.NotSupportedException was unhandled by user code
  Message=The expression ((((Parse([10007].fn_Latitude) >= 24.7614342656583) And (Parse([10007].fn_Latitude) <= 24.7686757343417)) And (Parse([10007].fn_Longitude) >= -80.0667877343417)) And (Parse([10007].fn_Longitude) <= -80.0595462656583)) is not supported.

如何使用数字的字符串值来大于或小于？

How can I use a string value of numbers to do greater than, or less than?

推荐答案

第一个选项尝试将varchar / string类型转换为数据库表中的double。第二个选项是加载所有没有过滤器的记录集，并在内存中进行比较，这将严重影响性能。第三个选项增强LinqToSql以支持Double.Parse将sql转换为类似Cast（列名为double）。



请参考 http://stackoverflow.com/questions/5971521/linq-to-entities-does -not-recognition-the-method-double-parsesystem-string-met [ ^ ]

虽然这是针对实体框架的

first option try to convert the varchar / string type to double in database table. Second option is load all recordset without filter and compare in memory which will hit performance badly. Third option enhance LinqToSql to support Double.Parse to convert sql something like Cast(columnname as double) .

please refer http://stackoverflow.com/questions/5971521/linq-to-entities-does-not-recognize-the-method-double-parsesystem-string-met[^]
although this is for entity framework

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