Question

I just started on a project converting an application from raw ADO.NET and embedded SQL to Entity. I ran in to a problem with one of the views used by the application. The view has no primary key and no column (or combination of columns) that uniquely identifies a row. Here is the select the view is created with:

SELECT
    filingmonth,
    CEIL(filingmonth / 3),
    licnum,
    filingyear,
    DECODE(GROUPING(insurername), '1', '- All Insured -', insurername),
    insurername,
    policylinecode,
    linedescription,
    SUM(NVL(grosspremium, 0)),
    SUM(DECODE(taxexempt, 1, grosspremium, 0)),
    TRUNC(
      CASE
        WHEN
          (
            b.rsn IS NOT NULL
            OR A.zeroreport = 1
          )
          AND b.datereceived IS NULL
            THEN A.datereceived
        ELSE b.datereceived
      END),
    SUM(aip.iscompanyadmitted(b.naiccocode, b.naicalienid)),
    A.insuredid
  FROM
    aip.slbtransinsured A
  LEFT OUTER JOIN aip.slbtransinsurer b
  ON
    A.insuredid = b.insuredid
  LEFT OUTER JOIN aip.slblinecodes C
  ON
    b.policylinecode = C.linecode
  WHERE
    A.submitted = 1
  AND A.entryincomplete = 0
  GROUP BY
    licnum,
    filingmonth,
    filingyear,
    TRUNC(
      CASE
        WHEN
          (
            b.rsn IS NOT NULL
            OR A.zeroreport = 1
          )
          AND b.datereceived IS NULL
            THEN A.datereceived
        ELSE b.datereceived
      END),
    ROLLUP(insurername, aip.iscompanyadmitted(b.naiccocode, b.naicalienid),
    policylinecode, linedescription), A.insuredid;

And here is some sample data showing that there are some rows that are completely duplicated (rows 3 and 4):

FILINGMONTH CEIL(FILINGMONTH/3) LICNUM FILINGYEAR DECODE(GROUPING(INSURERNAME),'1','-ALLINSURED-',INSURERNAME)                                         INSURERNAME                                                                                          POLICYLINECODE LINEDESCRIPTION                                                                                                                                                                                          SUM(NVL(GROSSPREMIUM,0)) SUM(DECODE(TAXEXEMPT,1,GROSSPREMIUM,0)) TRUNC(CASEWHEN(B.RSNISNOTNULLORA.ZEROREPORT=1)ANDB.DATERECEIVEDISNULLTHENA.DATERECEIVEDELSEB.DATERECEIVEDEND) SUM(AIP.ISCOMPANYADMITTED(B.NAICCOCODE,B.NAICALIENID)) INSUREDID

      6                   2   8150       2007 SAVERS PROPERTY AND CASUALTY INSURANCE CO                                                            SAVERS PROPERTY AND CASUALTY INSURANCE CO                                                            17             OTHER LIABILITY                                                                                                                                                                                                            721.25                                       0 18-JUL-07                                                                                                                                                          0        81 
      6                   2   8150       2007 SAVERS PROPERTY AND CASUALTY INSURANCE CO                                                            SAVERS PROPERTY AND CASUALTY INSURANCE CO                                                            17                                                                                                                                                                                                                                        721.25                                       0 18-JUL-07                                                                                                                                                          0        81 
      6                   2   8150       2007 SAVERS PROPERTY AND CASUALTY INSURANCE CO                                                            SAVERS PROPERTY AND CASUALTY INSURANCE CO                                                                                                                                                                                                                                                                                                      721.25                                       0 18-JUL-07                                                                                                                                                          0        81 
      6                   2   8150       2007 SAVERS PROPERTY AND CASUALTY INSURANCE CO                                                            SAVERS PROPERTY AND CASUALTY INSURANCE CO                                                                                                                                                                                                                                                                                                      721.25                                       0 18-JUL-07                                                                                                                                                          0        81 

insuredid is the pk for the aip.slbtransinsured table, rsn is the pk for aip.slbtransinsurer and aip.slblinecodes.

Is it at all possible to add a view to the Entity model without a unique identifier? Or is there an easy way to add a unique row identifier to the view? The view is only read from, never written to.

Answer 1

Is it at all possible to add a view to the Entity model without a
unique identifier?

If without a primary key, no. That will result to this kind of error:

One or more validation errors were detected during model generation:

System.Data.Edm.EdmEntityType: : EntityType ‘SalesOnEachCountry’ has
no key defined. Define the key for this EntityType.
System.Data.Edm.EdmEntitySet: EntityType: The EntitySet
SalesOnEachCountryList is based on type SalesOnEachCountry that has no
keys defined.

If without a unique identifier, yes, albeit it has a non-desirable output. Records with same identifier would reference the same object, this is called Identity Map Pattern

An example, even if your view produces these two rows:

Country     Year TotalSales
Philippines 2010 20.000000
Philippines 2011 40.000000

If you will just map the primary key on Country field only, e.g.

public class SalesOnEachCountry
{        
    [Key]
    public int CountryId { get; set; }
    public string CountryName { get; set; }        
    public int OrYear { get; set; }
    public long SalesCount { get; set; }
    public decimal TotalSales { get; set; }
}

, even your view produces the above two rows on your Oracle query editor, Entity Framework produces this incorrect output:

Country     Year TotalSales
Philippines 2010 20.000000
Philippines 2010 20.000000

Entity Framework will take it that the second row is same object as first row.

To guarantee uniqueness, you must identify what columns that makes each row unique. In the above example, Year must be included so the primary key is unique. i.e.

public class SalesOnEachCountry
{        
    [Key, Column(Order=0)] public int CountryId { get; set; }
    public string CountryName { get; set; }
    [Key, Column(Order=1)] public int OrYear { get; set; }

    public long SalesCount { get; set; }      
    public decimal TotalSales { get; set; }
}

Making your primary key similar to the attributes above, Entity Framework can correctly map your each view’s row to their own objects. Hence, Entity Framework can now display exactly the same rows your view have.

Country     Year TotalSales
Philippines 2010 20.000000
Philippines 2011 40.000000

Full details here: http://www.ienablemuch.com/2011/06/mapping-class-to-database-view-with.html

---

Then regarding your views which don’t have any columns to make a row unique, the easiest way to guarantee Entity Framework can map each of your view’s row to their own objects is to create a separate column for your view’s primary key, a good candidate is to just create a row number column on each row. e.g.

create view RowNumberedView as

select 
    row_number() over(order by <columns of your view sorting>) as RN
    , *
from your_existing_view

Then assign the [Key] attribute on RN property of your class RowNumberedView