为什么此LinQ查询不喜欢字符? [英] Why does this LinQ query not like chars?

问题描述

我有一个LINQ查询，它可以获取所需的所有数据并将其合并到数据传输对象中，一切正常，除了当我将DTO的一个成员(即char)设置为char值时会引发查询异常...

I have a LINQ query that grabs all the data it needs and consolidates it into a data transfer object, everything works fine EXCEPT it throws query exceptions when I set one of the DTO's members (which is a char) to a char value...

类型为'System.ServiceModel.FaultException'的未处理异常 发生在mscorlib.dll

An unhandled exception of type 'System.ServiceModel.FaultException' occurred in mscorlib.dll

无法创建类型为'System.Char'的常量值.在这种情况下，仅支持基本类型或枚举类型.

Unable to create a constant value of type 'System.Char'. Only primitive types or enumeration types are supported in this context.

请参见下面的简化查询:

See the simplified query below:

var result = (from c in db.Foster_Carers
              where c.foster_carer_id == id
              join fc in db.Individual_Carers on c.first_carer_id equals fc.individual_carer_id
              select new FosterCarerPersonalInfoDTO
              {
                  carer_title = fc.title,
                  carer_forenames = fc.forename,
                  carer_surname = fc.surname,                                
                  carer_gender = 'm'
              }).SingleOrDefault();

将性别设置为'm'只是行不通，从语法上讲还可以，只是在执行查询时不行！可能是什么问题?

Setting the gender to 'm' just won't work, syntactically it is okay, just not when the query is executed! What could be the issue?

推荐答案

这是EF的局限性，因为char不是原始类型，请参见此答案来映射字符的属性，以获取有关原因的更多详细信息.该限制本身也已记录.

This is a limitation of EF because char is not a primitive type, see this answer for more details as to why. The limitation itself is also documented.

我建议您只使用string.

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