Question

I have three tables A, B, C. A having Id,Name,Address coulmns. B is the generic table having attributeID,aId, attributeName. where as c is the details table for B. with columns valueId, attributeId, aId Value.
Scenario is. suppose A is the Specific entity table (say Student). only containing the basic columns and values. where as B is there for additional columns for Entity student. (ex, student may have changed address, may have 3 mobile numbers)

    Table: A
    Aid      Name                   Address1 
    std1     Student                MG Street
    std2     Employee               Royal Street

    Table : B
    attributeId    aID            Value
    att1           std1          Address2
    att2           std1          ChangedAddress   
    att3           std1          Mobile1
    att4           std1          Mobile2

Table :C
 ValueId  attributeId    aID            Value

val1      att1           std1          Stefen colony  
val2      att2           std1          ChangedTo:Laurds
val3      att3           std1          87879797979798
val4      att4           std1          544559797979798


Note :Same for Employee 

I want to build the query to get the all the valuefrom c for std1 with values in table A. But somehow db stucture is dynamic, in the sence the coulmns for the table A stored as values in table B, where as Values for B attributes stored in Table C. How to write Linq query for this?

Answer 1

You can simply join the records together like:

class Student
{
    public int Id { get;set;}
}

class StudentPropertyDefintion
{
    public int Id { get; set; }
    public int StudentId { get; set; }
    public string PropertyName { get; set; }
}

class StudentPropertyValue
{
    public int PropertyDefinitionId { get; set; }
    public string PropertyValue { get; set; }
}

class Context
{
    public ISet<Student> Students { get; set; }
    public ISet<StudentPropertyDefintion> PropertyDefinitions { get; set; }
    public ISet<StudentPropertyValue> PropertyValues { get; set; }
}

// and query that

  Context context = new Context();

        var studentWithPropertiesQuery = from student in context.Students
                                         join propertyDefinition in context.PropertyDefinitions
                                         on student.Id equals propertyDefinition.StudentId
                                         join propertyValue in context.PropertyValues
                                         on propertyDefinition.Id equals propertyValue.PropertyDefinitionId
                                         select new
                                         {
                                             propertyValue,
                                             propertyDefinition,
                                             student
                                         };