LINQ ICollection of a Model to a string with Name and Surname from within another model

Question

I have a field which is a collection of a model ICollection "Parties", which is in another model "Matter". I want to extract the Name and Surname of each party and separate with a "/" using LINQ. I am putting these into a field called Investors, the second last item.

This is my query:

    var matterQuery = (from matter in context.Matters
  select new
  {
      matter.ID,
      matter.AttorneyRef,
      matter.Status,
      matter.ProductType,
      matter.IsDiscarded,
      matter.Base_CreatedDate,
      matter.Base_CreatedBy,
      matter.BranchID,
      matter.InstitutionID,
      matter.InvestmentTypeID,

      StatusName = matter.MatterStatu != null ? matter.MatterStatu.Name : string.Empty,
      ProductTypeName = matter.ProductType1 != null ? matter.ProductType1.Name : string.Empty,
      AccountNumber = matter.Account != null ? matter.Account.AccountNumber : string.Empty,
      CreatedBy = matter.Paralegal != null ? matter.Paralegal 
      : matter.AspNetUser != null ? matter.AspNetUser.FirstName + " " + matter.AspNetUser.LastName
      : matter.User != null ? matter.User.Firstname + " " + matter.User.Surname
      : string.Empty,
      IntermediaryName = matter.IntermediaryBranch != null ? matter.IntermediaryBranch.Intermediary.Name 
      : matter.Attorney != null ? matter.Attorney.AttorneyName
      : string.Empty,
      CloseRequested = matter.CloseAccounts.Where(x => x.Status == (int)CloseAccountStatusEnum.Authorised).Count() > 0,
      StatementRequested = matter.Account != null ? matter.Account.StatementRequested : false,
      RequestedDate = matter.RequestedDate.HasValue ? matter.RequestedDate.Value : matter.Base_CreatedDate,
      Investors = matter.Parties.Select(x => x.Name.ToString()).Concat(matter.Parties.Select(x => x.Surname.ToString())),
      SoftLock = matter.SoftLock,
  })
   .AsQueryable();

I need this in 1 long string as I am doing a search on the results for a filter and the following line:

(x.Investors != null && x.Investors.ToLower().Contains(search))

requires it be in a string format. I want to display the results as "Name1 Surname1 / Name2 Surname2 / ..."

How can I do this?

EDIT:

I have tried Join and Aggregate but I get the errors:

base {System.SystemException} = {System.NotSupportedException: LINQ to Entities does not recognize the method 'System.String Join(System.String, System.Collections.Generic.IEnumerable`1[System.String])' method, and this method cannot be translated into a store expression. at System.Da...

and...

System.NotSupportedException: LINQ to Entities does not recognize the method 'System.String Aggregate[String](System.Collections.Generic.IEnumerable1[System.String], System.Func3[System.String,System.String,System.String])'

Answer 1

I solved this by:

In the original query:

select new{
Investors = matter.Parties.Select(x => x.Name + " " + x.Surname), 
}

In the search:

matterQuery.Where(x =>
(x.Investors.Any(y => y.ToLower().Contains(searchString)))
);

When transferring data to a ViewModel:

Investors = String.Join(" / ", matter.InvestorNames),