LINQ where子句引发第二个where的错误

更新

即使在联系人firstName或LastName上进行搜索也会导致问题：

var contacts =
            (
                from c in context.ContactSet
                join m in context.py3_membershipSet on c.ContactId equals m.py3_Member.Id
                where m.statuscode.Value == 1
                && ((c.FirstName != null && c.FirstName == searchTerm) || (c.LastName!=null && c.LastName == searchTerm) || (c.FullName != null && c.FullName == searchTerm))  
                orderby c.LastName
                select new
                {
                    ContactId = c.ContactId,
                    FirstName = c.FirstName,
                    LastName = c.LastName,
                    BranchCode = c.py3_BranchArea,
                    Branch = (c.FormattedValues != null && c.FormattedValues.Contains("py3_brancharea") ? c.FormattedValues["py3_brancharea"] : "N/a"),
                    JobTitle = c.JobTitle,
                    Organisation = (c.ParentCustomerId != null ? c.ParentCustomerId.Name : "N/a"),
                    joinedAsCode = c.py3_SOLACEMemberJoinedAs,
                    JoinedAs = (c.FormattedValues != null && c.FormattedValues.Contains("py3_solacememberjoinedas") ? c.FormattedValues["py3_solacememberjoinedas"] : "N/a"),
                    Expertise = (c.py3_SOLACEMemberAreasofExpertise != null && c.py3_SOLACEMemberAreasofExpertise.Trim() != String.Empty ? c.py3_SOLACEMemberAreasofExpertise : "N/a"),
                    Title = c.Salutation
                }
            );

它尖叫着回应：

"py3_membership"实体不包含Name="firstname"的属性。

我收到了以下代码，其中包含一些来自在线CRM的信息：

        var context = new XrmServiceContext();
    var contacts1 =
        (
            from c in context.ContactSet
            join m in context.py3_membershipSet on c.ContactId equals m.py3_Member.Id
            where m.statuscode.Value == 1
            orderby c.LastName
            select new
            {
                ContactId = c.ContactId,
                FirstName = c.FirstName,
                LastName = c.LastName,
                BranchCode = c.py3_BranchArea,
                Branch = (c.FormattedValues != null && c.FormattedValues.Contains("py3_brancharea") ? c.FormattedValues["py3_brancharea"] : "N/a"),
                JobTitle = c.JobTitle,
                Organisation = (c.ParentCustomerId != null ? c.ParentCustomerId.Name : "N/a"),
                joinedAsCode = c.py3_SOLACEMemberJoinedAs,
                JoinedAs = (c.FormattedValues != null && c.FormattedValues.Contains("py3_solacememberjoinedas") ? c.FormattedValues["py3_solacememberjoinedas"] : "N/a"),
                Expertise = (c.py3_SOLACEMemberAreasofExpertise != null && c.py3_SOLACEMemberAreasofExpertise.Trim() != String.Empty ? c.py3_SOLACEMemberAreasofExpertise : "N/a")
            }
        );

然后，我将其作为数组绑定到数据列表，这一切都很好。

然而，我希望能够将结果限制在从下拉列表中选择的值，并期望以下内容起作用：

        var context = new XrmServiceContext();
    var contacts1 =
        (
            from c in context.ContactSet
            join m in context.py3_membershipSet on c.ContactId equals m.py3_Member.Id
            where m.statuscode.Value == 1 &&
                c.FormattedValues["py3_brancharea"] == ddlBranchTags.SelectedItem.Value

            orderby c.LastName
            select new
            {
                ContactId = c.ContactId,
                FirstName = c.FirstName,
                LastName = c.LastName,
                BranchCode = c.py3_BranchArea,
                Branch = (c.FormattedValues != null && c.FormattedValues.Contains("py3_brancharea") ? c.FormattedValues["py3_brancharea"] : "N/a"),
                JobTitle = c.JobTitle,
                Organisation = (c.ParentCustomerId != null ? c.ParentCustomerId.Name : "N/a"),
                joinedAsCode = c.py3_SOLACEMemberJoinedAs,
                JoinedAs = (c.FormattedValues != null && c.FormattedValues.Contains("py3_solacememberjoinedas") ? c.FormattedValues["py3_solacememberjoinedas"] : "N/a"),
                Expertise = (c.py3_SOLACEMemberAreasofExpertise != null && c.py3_SOLACEMemberAreasofExpertise.Trim() != String.Empty ? c.py3_SOLACEMemberAreasofExpertise : "N/a")
            }
        );

然而，这会引发以下错误：

Invalid 'where' condition. An entity member is invoking an invalid property or method.

即使我硬编码branchtag条件而不是去DDL值，它也是一样的。我还试着在联系人1上进行了选择，例如：

var results = contacts1.select(c=> c.BranchTag == ddlBranchTags.SelectedItem.Value

但这也带来了同样的错误。

如果我删除branchTag where子句，它将按预期工作。我认为可以公平地假设我在这方面很任性，所以任何有用/建设性的建议(对于LINQ新手(都将非常感激。谢谢