表达式-无法创建类型为'System.Collections.Generic.List`1'的常量值。 仅原始类型（例如Int32，String和Gu

Question

I have written following lambda expression

Expression<Func<ContractObject, bool>> objExpression = 
i => i.ContractProjects.Any(a => ProjectList.Any(p => p.Id == a.ProjectId));

ContractProjects and ProjectList are List of two different types sharing common values ie. ProjectId and Id respectively.

But it is throwing following exception. Is there any changes that I have to do or can this expression be written in some another way?

Unable to create a constant value of type 'System.Collections.Generic.List`1'. Only primitive types ('such as Int32, String, and Guid') are supported in this context.

Answer 1

I think the problem is that your ContractList might not have been created yet

try :

var objExpression = i => i.ContractProjects.ToList()
                          .Any(a => ProjectList.Any(p => p.Id == a.ProjectId));

Answer 2

After many trial and error I got the following solution as follows

List<Int32> projectIds = new List<Int32>();

foreach (Project p in ProjectList)
    projectIds.Add(p.Id);

Expression<Func<ContractObject, bool>> objExpression = 
i => i.ContractProjects.Any(a => projectIds.Contains(a.ProjectId)));

Thanks for helping