具有多个字段的LINQ DistinctBy不包含DistinctBy的定义

Question

我想在此LINQ语句的四个字段中添加DistinctBy，但出现一些错误，其中不包含DistinctBy的定义。我需要导入一个类吗？

    public IQueryable<TemplatesJoinAgent> GetTemplateAgentKeyDiseaseId(Guid? agentKey, Guid? diseaseId)
    {
        //Common part
        var TemplatesJoinAgent = (from t in UnitOfWork.GetRepository<Template>().Get()
                    join r in UnitOfWork.GetRepository<Regimen>().Get() on t.Id equals r.TemplateId
                    join rp in UnitOfWork.GetRepository<RegimenPart>().Get() on r.Id equals rp.RegimenId
                    join re in UnitOfWork.GetRepository<RegimenEntry>().Get() on rp.Id equals re.RegimenPartId
                    join a in UnitOfWork.GetRepository<Agent>().Get() on re.AgentVersionKey equals a.VersionKey
                    where t.IsCurrentVersion && t.Status==7 && a.IsCurrentVersion
                    select new TemplatesJoinAgent
                    {
                        Template = t,

                        Agent = a

                    });

        //Extra filters
        if (agentKey != null)
        {
            TemplatesJoinAgent = TemplatesJoinAgent.Where(o => o.Agent.VersionKey == agentKey);
        }
        if (diseaseId != null)
        {
            TemplatesJoinAgent = TemplatesJoinAgent.Where(o => o.Template.ExternalDiseaseId == diseaseId);
        }

        TemplatesJoinAgent = TemplatesJoinAgent.DistinctBy(x => t.DiseaseName).ToList();

        return TemplatesJoinAgent;
    }

Answer 1

正如其他人所提到的，DistinctBy不是标准LINQ函数的一部分。但是，您可以通过实现自己的DistinctBy扩展来添加此功能。像这样的人可以完成这项工作：

public static class IEnumerableExtensions
    {
        public static IEnumerable<TSource> DistinctBy<TSource,TKey>(this IEnumerable<TSource> source, Func<TSource, TKey> selector)
        {
            var keys = new HashSet<TKey>();
            foreach (TSource item in source)
            {
                if (keys.Add(selector(item)))
                    yield return item;
            }
        }
    }