How to convert this query from sql to linq-to-entities

Question

How to convert following query from sql(Oracle) to linq-to-entities:

select * FROM ActivityPromptText where ActivityId = 8 
         and ProcessTypeId = 1 and ProcessId is null

When I am writing this c#, its returning null, while same query is returning result in sql. The Linq query is:

var text2 = this.context.ActivityPromptText
       .Where(pt => (pt.ActivityId == activityId && pt.ProcessTypeId == processType) 
                      && pt.ProcessId == null)
      .Include(pt => pt.Prompt).FirstOrDefault();

=======================

The MODELS are:

[Table("ActivityPromptText")]
public class ActivityPromptText
{
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.None)]
    [Column(Order = 1)]
    public int PromptTextId { get; set; }

    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.None)]
    [Column(Order = 2)]
    public int ActivityId { get; set; }

    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.None)]
    [Column(Order = 3)]
    public int ProcessTypeId { get; set; }

    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.None)]
    [Column(Order = 4)]
    public int? ProcessId { get; set; }

    [ForeignKey("PromptTextId")]
    public virtual PromptText MbopPrompt { get; set; }
}

and:

[Table("PromptText")]
public class PromptText
{
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.None)]
    public int PromptTextId { get; set; }

    public string PromptText { get; set; }

}

and The DBContext file has:

public virtual DbSet ActivityPromptTexts { get; set; }

public virtual DbSet PromptTexts { get; set; }

Answer 1

I think the problem is the Key attribute for your ProcessId property. Keys can't be null i think, are they really keys or rather indexes? If they're indexes and you're using EF6.1+ : http://msdn.microsoft.com/en-us/data/jj591583.aspx#Index

Multi-column indexes are also supported.