Linq, Unable to Create a Constant Value of Type Xxx. Only Primitive Types or Enumeration Types Are Supported in This Context

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

This cannot work because ppCombined is a collection of objects in memory and you cannot join a set of data in the database with another set of data that is in memory. You can try instead to extract the filtered items personProtocol of the ppCombined collection in memory after you have retrieved the other properties from the database:

var persons = db.Favorites
    .Where(f => f.userId == userId)
    .Join(db.Person, f => f.personId, p => p.personId, (f, p) =>
        new // anonymous object
        {
            personId = p.personId,
            addressId = p.addressId,   
            favoriteId = f.favoriteId,
        })
    .AsEnumerable() // database query ends here, the rest is a query in memory
    .Select(x =>
        new PersonDTO
        {
            personId = x.personId,
            addressId = x.addressId,   
            favoriteId = x.favoriteId,
            personProtocol = ppCombined
                .Where(p => p.personId == x.personId)
                .Select(p => new PersonProtocol
                {
                    personProtocolId = p.personProtocolId,
                    activateDt = p.activateDt,
                    personId = p.personId
                })
                .ToList()
        });

LINQ Query error: Unable to create a constant value of type. Only primitive types or enumeration types are supported in this context

endedContracts is an in memory list and cannot be used directly in this query. Instead, get the value you need outside of the query, for example:

//Get the code here
var brokerCode = endedContracts.First().Broker.Code;

var crystallisedCommissions = _context.Contracts
   .Where(x => x.Statement.Sent)
   .Where(x => x.Statement.Broker == brokerCode) //Use the code here
   .Where(x => !Period.IsPeriodBeforeReferencePeriod(x.Statement.Period, CUT_OFF_PERIOD))
   .Where(x => endedContracts.Any(y => y.Contract.Identifier == x.Identifier
                                    && y.Contract.StartDate == x.ContractStartDate
                                    && y.Contract.EndDate == x.ContractEndDate)).ToList();

LINQ, Unable to create a constant value of type XXX. Only primitive types or enumeration types are supported in this context

You can't use Contains with non-primitive values. Do

Where(l => l.Courses.Select(c => c.CourseId).Contains(courseId)

(or the Id field you use).

Unable to create a constant value - only primitive types

First way :

Remove ToList() in the first query.

Or

//instead of retrieving mathings List, retrieve only the productIds you need (which are a List of Primitive types)
var productIdList = db.matchings
.Where(m => m.StoreId == StoreId)
.Select(x => x.ProductId)
.ToList();

var products = db.Products
.Where(p => productIdList
           .Contains(p.ProductId))
.ToList();

Or

//other way
var produts = db.Products
             .Where(p => db.matchings
                        .Any(m => m.StoreId == StoreId && 
                             m.ProductId == p.ProductId)
                    )
             .ToList();

Because I think you're in linq2entities, and you're using a List of Matchings in a query which is not possible (the title of your topic tend to make me believe that's your problem).

C# - Linq : Unable to create a constant value of type Only primitive types or enumeration types are supported in this context.

The exception message is quite descriptive.

DefaultIfEmpty(new Person_Login({Id = -1})

is not supported in Linq to Entities.

You can use the following instead

var login = context.Person_Login
    .FirstOrDefault(c => c.Username == username && c.Password == password)
    ?? new Person_Login {Id = -1};

Note that DefaultIfEmpty method is used mainly for performing LINQ left outer joins.

Linq Any - Only primitive types or enumeration types are supported in this context

Try:

if (medico.Especialidad.Count > 0)
{
    var medicoId = medico.Especialidad.FirstOrDefault().ID
    listaMedicos = FiltrarPor(listaMedicos, 
        x => x.Especialidad.Any(e => e.ID == medicoId));
}

actually, better, would be:

var medicoEspecialidad = medico.Especialidad.FirstOrDefault();
if (medicoEspecialidad != null)
{
    var medicoId = medicoEspecialidad.ID
    listaMedicos = FiltrarPor(listaMedicos, x => x.Especialidad.Any(e => e.ID == medicoId));
}

Unable to create a constant value of type (type) Only primitive types ('such as Int32, String, and Guid') are supported in this context

It will not work because you want to use local Album in linq-to-entities query. You must either use navigation property on p to get its album:

var query = from p in VisibleObjects.OfType<Photo>()
            where p.Album.Id == alb.Id
            select p;

or you must build complex query with some join between photos and albums. You cannot pass local object and any its relation to the query. Only simple properties can be passed.

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