Making stringly-typed code palatable via implicit operator

Bad programmers worry about the code. Good programmers worry about data structures and their relationships.

-- http://programmers.stackexchange.com/questions/163185/torvalds-quote-about-good-programmer

Smart data structures and dumb code works a lot better than the other way around.

-- Eric S. Raymond


Strongly-typed code is all the rage now, but some of us still manages to stash various information to string instead of structuring the information to a class.



But if you are in an unfortunate codebase and it has a dumb data structure to begin with, e.g., it has stringly-typed data, at least make a smart data structure facade. Not only smart data structure is easy to code on, it can make the codes that depends on the smart data structure very simple, smaller and easy to read.

using System;

using System.Collections.Generic;


using System.Linq;


namespace Craft
{
    class MainClass
    {

        public static void Main (string[] args)
        {
            var list = new Dictionary<string,decimal> ();
            list.Add ("1_VariablePayBasis", 1337);
            list.Add ("1_DecisionAmount", 168);
            list.Add ("3_BasePay", 5201314);


            // Dumb data structure. Smart code.

            foreach (var kv in list) {

                // boilerplate codes. a.k.a. Smart Code
                string[] strings = kv.Key.Split('_');
                int pk = Convert.ToInt32(strings [0]);
                string fieldName = strings [1];


                Console.WriteLine ("{0} {1} - {2}", pk, fieldName, kv.Value);
            }
            Console.WriteLine();


            
            // Smart data structure. Dumb code.

            // via explicit casting, being explicit with implicit :-)
            foreach (var fv in list.Select(x => (FieldValue)x)) {
                Console.WriteLine ("{0} {1} - {2}", fv.PrimaryKey, fv.FieldName, fv.Value);
            }
            Console.WriteLine();



            // Smart data structure. Dumb code.

            // neat implicit! it still feel a bit explicit though. we can't use var here
            foreach (FieldValue fv in list) {
                Console.WriteLine ("{0} {1} - {2}", fv.PrimaryKey, fv.FieldName, fv.Value);
            }

        }
    }

    public class FieldValue
    {
        public int PrimaryKey { get; set; }
        public string FieldName { get; set; }

        public decimal Value { get; set; }



        public static implicit operator FieldValue(KeyValuePair<string,decimal> kv)
        {
            string[] strings = kv.Key.Split('_');
            int pk = Convert.ToInt32(strings [0]);
            string fieldName = strings [1];

            return new FieldValue { PrimaryKey = pk, FieldName = fieldName, Value = kv.Value };
        }
    }
   
}

Live Code https://dotnetfiddle.net/qX2UeA


Happy Coding! ツ

protected internal

Anne Epstein has a great NHibernate article on making an entity with a composite primary key be lazy-loading-capable and cache-ready. Just forgot to hide the ORM low-level plumbing concerns (the composite primary key) from the domain model


Similar to AdventureWorks' EmployeePayHistory. Just use protected internal to hide that ORM low-level plumbing concern

public class PersonPayHistory
{
    PersonPayHistoryCompositePK _pk = new PersonPayHistoryCompositePK();
    protected internal PersonPayHistoryCompositePK PersonPayHistoryCompositePK 
    { 
        get { return _pk; }
        set { _pk = value; }
    }

    Person _person;
    public virtual Person Person 
    { 
        get { return _person; }
        set 
        {
            _person = value;
            _pk.PersonId = _person.PersonId;
        }
    }                    

    public virtual DateTime RateDate
    {
        get { return _pk.RateDate; }
        set { _pk.RateDate = value; }
    }

    public virtual decimal Rate { get; set; }
}

So we will not make the mistake of saving our entity through those composite primary key:

var ph = new PersonPayHistory
{     
    Person = session.Load<Person>(1),
    RateDate = DateTime.Today,

    Rate = 1337M
};


session.Save (ph);
session.Flush ();

LEFT JOIN GROUP BY HAVING on NHibernate

EmployeePayHistory payHistory = null;
   
var persons =
    session.QueryOver<Person>()
    .Left.JoinAlias(p => p.PayHistories, () => payHistory)                        
    .Where(
        Restrictions.Eq(
            Projections.Count(() => payHistory.EmployeePayHistoryCompositePK.BusinessEntityId)
        , 0
        )
    )    
    .SelectList(x => x
        .SelectGroup(p => p.BusinessEntityId)
        .SelectGroup(p => p.FirstName)
        .SelectGroup(p => p.LastName)                            
        .SelectCount(p => payHistory.EmployeePayHistoryCompositePK.BusinessEntityId)
    )
    .List<object[]>()
    .Select(cols => new
    {
        Id = (int)cols[0],
        FirstName = (string)cols[1],
        LastName = (string)cols[2],
        Count = (int)cols[3]
    });

persons.ToList();

Generated SQL:

SELECT
         this_.BusinessEntityId as y0_,
         this_.FirstName as y1_,
         this_.LastName as y2_,
         count(payhistory1_.BusinessEntityId) as y3_
     FROM
         Person.Person this_
     left outer join
         HumanResources.EmployeePayHistory payhistory1_
             on this_.BusinessEntityId=payhistory1_.BusinessEntityId
     GROUP BY
         this_.BusinessEntityId,
         this_.FirstName,
         this_.LastName
     HAVING
         count(payhistory1_.BusinessEntityId) = @p0;
     @p0 = 0 [Type: Int32 (0)]

One-stop shop code, complete working code. Just install AdventureWorks2008R2 database:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

using NHibernate.Cfg;
using NHibernate.Cfg.MappingSchema;
using NHibernate.Criterion;
using NHibernate.Mapping.ByCode.Conformist;
 
using NHibernate.Linq;

 
namespace Craft
{
    class Program
    {
        static void Main(string[] args)
        {
            using (var session = Mapper.SessionFactory.OpenSession())
            {
                
         EmployeePayHistory payHistory = null;

         var persons =
                     session.QueryOver<Person>()
                    .Left.JoinAlias(p => p.PayHistories, () => payHistory)
                    .Where(
                         Restrictions.Eq(
                             Projections.Count(() => payHistory.EmployeePayHistoryCompositePK.BusinessEntityId)
                             , 0
                         )
                     )

                    .SelectList(x => x
                        .SelectGroup(p => p.BusinessEntityId)
                        .SelectGroup(p => p.FirstName)
                        .SelectGroup(p => p.LastName)                            
                        .SelectCount(p => payHistory.EmployeePayHistoryCompositePK.BusinessEntityId)
                    )
                   .List<object[]>()
                   .Select(cols => new
                   {
                      Id = (int)cols[0],
                      FirstName = (string)cols[1],
                      LastName = (string)cols[2],
                      Count = (int)cols[3]
                   });

                persons.ToList();



                Console.ReadLine();
           } // using
        } // Main
    } //class Program
 
 
    public static class Mapper
    {
        static NHibernate.ISessionFactory _sessionFactory = Mapper.GetSessionFactory();
 
 
        public static NHibernate.ISessionFactory SessionFactory
        {
            get { return _sessionFactory; }
        }
 
        static NHibernate.ISessionFactory GetSessionFactory()
        {
            var mapper = new NHibernate.Mapping.ByCode.ModelMapper();
 
            mapper.AddMappings(
                new[] { 
                    typeof(PersonMapping) , typeof(EmployeePayHistoryMapping)
                });
 
 
            var cfg = new NHibernate.Cfg.Configuration();
 
            cfg.DataBaseIntegration(c =>
            {
                c.Driver<NHibernate.Driver.Sql2008ClientDriver>();
                c.Dialect<NHibernate.Dialect.MsSql2008Dialect>();
                c.ConnectionString = "Server=.;Database=AdventureWorks2008R2;Trusted_Connection=True;";
 
                c.LogFormattedSql = true;
                c.LogSqlInConsole = true;
            });
 
 
 
            HbmMapping domainMapping = mapper.CompileMappingForAllExplicitlyAddedEntities();
 
            cfg.AddMapping(domainMapping);
 
 
 
            var sf = cfg.BuildSessionFactory();
 
            return sf;
        }
    }
 
 
    public class PersonMapping : ClassMapping<Person>
    {
        public PersonMapping()
        {
            Table("Person.Person");
            Id(x => x.BusinessEntityId);
 
            Property(x => x.FirstName);
            Property(x => x.LastName);
 
            Bag(list => list.PayHistories, rel => rel.Key(k => k.Column("BusinessEntityId")), relType => relType.OneToMany());
 
        }
    }
 
    public class EmployeePayHistoryMapping : ClassMapping<EmployeePayHistory>
    {
        public EmployeePayHistoryMapping()
        {
            Table("HumanResources.EmployeePayHistory");
 
            ComponentAsId(x => x.EmployeePayHistoryCompositePK, x =>
            {
                x.Property(y => y.BusinessEntityId);
                x.Property(y => y.RateChangeDate);
            });
          
            ManyToOne(x => x.Person, k => 
            { 
                k.Column("BusinessEntityId"); 
                k.Insert(false); 
                k.Update(false); 
            });

            Property(x => x.Rate);
        }
    }
 
    
 
    public class Person
    {
        public virtual int BusinessEntityId { get; set; }
        public virtual string FirstName { get; set; }
        public virtual string LastName { get; set; }
 
        public virtual IList<EmployeePayHistory> PayHistories { get; set; }
    }
 
 
    public class EmployeePayHistory
    {
        EmployeePayHistoryCompositePK _pk = new EmployeePayHistoryCompositePK();
        public virtual EmployeePayHistoryCompositePK EmployeePayHistoryCompositePK 
        { 
            get { return _pk; } set { _pk = value; }
        }
 
        Person _person;
        public virtual Person Person 
        { 
            get { return _person; }
            set 
            {
                _person = value;
                _pk.BusinessEntityId = _person.BusinessEntityId;
            }
        }        
 
        public virtual decimal Rate { get; set; }
    }
 
 
    // AdventureWorks is fond of composite primary key. Composite unique is better
    public class EmployeePayHistoryCompositePK
    {
        public virtual int BusinessEntityId { get; set; }
        public virtual DateTime RateChangeDate { get; set; }
 
        public override bool Equals(object obj)
        {
            if (obj == null)
                return false;
 
            var t = obj as EmployeePayHistoryCompositePK;
            if (t == null)
                return false;
 
            if (BusinessEntityId == t.BusinessEntityId && RateChangeDate == t.RateChangeDate)
                return true;
 
            return false;
        }
 
        public override int GetHashCode()
        {
            return (BusinessEntityId + "|" + RateChangeDate).GetHashCode();
        }
    }
}

Happy Coding! ツ


Related: http://www.ienablemuch.com/2014/07/orm-expectations.html

ORM Expectations

Sometimes it's hard to give clear instruction, especially if you are not inclined to be exact with your instruction:

var persons = 
     from p in session.Query<Person>()
     select new 
     {
         p.BusinessEntityId, p.FirstName, p.LastName, Count = p.PayHistories.Count()
     };

What's the SQL generated by that Linq?

NHibernate-generated SQL:
 
select
    person0_.BusinessEntityId as col_0_0_,
    person0_.FirstName as col_1_0_,
    person0_.LastName as col_2_0_,
    (select
        cast(count(*) as INT)
    from
        HumanResources.EmployeePayHistory payhistori1_
    where
        person0_.BusinessEntityId=payhistori1_.BusinessEntityId) as col_3_0_
from
    Person.Person person0_                    
 
 
Entity Framework-generated SQL:
 
SELECT 
    [Extent1].[BusinessEntityId] AS [BusinessEntityId],
    [Extent1].[LastName] AS [LastName],
    [Extent1].[FirstName] AS [FirstName],
    (SELECT
        COUNT(1) AS [A1]
    FROM 
        [HumanResources].[EmployeePayHistory] AS [Extent2]
    WHERE 
        [Extent1].[BusinessEntityId] = [Extent2].[BusinessEntityId]) AS [C1]
FROM 
    [Person].[Person] AS [Extent1]

"That's not efficient! That's not what I wanted" you told yourself

I've often felt that much of the frustration with ORMs is about inflated expectations -- http://martinfowler.com/bliki/OrmHate.html

There are developers who insists that the above should generate a GROUP BY COUNT. Don't expect a GROUP BY will be generated on the Linq you've made above. Who told you that computers will do what you wanted or hoped them to do? You cannot wish your way around on solving a problem, especially on giving instructions to computers

With that being said, let's be exact with our instructions. Let's cut to the chase, following is how to do efficient aggregation in NHibernate and Entity Framework. Initial step, flatten the hierarchical objects via SelectMany; final step, do a group by on the flattened object. Easy-peasy!

var persons =
    from p in session.Query<Person>()
        .SelectMany(x => x.PayHistories, (person, payHistory) => new {person, payHistory})
    group p by new {p.person.BusinessEntityId, p.person.FirstName, p.person.LastName} into g
    select new {g.Key, Count = g.Count()};

SQL output:

NHibernate-generated SQL:
 
select
    person0_.BusinessEntityId as col_0_0_,
    person0_.FirstName as col_1_0_,
    person0_.LastName as col_2_0_,
    cast(count(*) as INT) as col_3_0_
from
    Person.Person person0_
inner join
    HumanResources.EmployeePayHistory payhistori1_
        on person0_.BusinessEntityId=payhistori1_.BusinessEntityId
group by
    person0_.BusinessEntityId ,
    person0_.FirstName ,
    person0_.LastName
 

Entity Framework-Generated SQL. Go home Entity Framework, you're drunk!

SELECT
    [GroupBy1].[K1] AS [BusinessEntityId],
    [GroupBy1].[K4] AS [C1],
    [GroupBy1].[K3] AS [FirstName],
    [GroupBy1].[K2] AS [LastName],
    [GroupBy1].[A1] AS [C2]
    FROM ( SELECT
        [Join1].[K1] AS [K1],
        [Join1].[K2] AS [K2],
        [Join1].[K3] AS [K3],
        [Join1].[K4] AS [K4],
        COUNT([Join1].[A1]) AS [A1]
        FROM ( SELECT
            [Extent1].[BusinessEntityId] AS [K1],
            [Extent1].[LastName] AS [K2],
            [Extent1].[FirstName] AS [K3],
            1 AS [K4],
            1 AS [A1]
            FROM  [Person].[Person] AS [Extent1]
            INNER JOIN [HumanResources].[EmployeePayHistory] AS [Extent2] ON [Extent1].[BusinessEntityId] = [Extent2].[BusinessEntityId]
        )  AS [Join1]
        GROUP BY [K1], [K2], [K3], [K4]
    )  AS [GroupBy1]

With the exact instructions, the computer will do what we told it to do, NHibernate generated what we wanted, a COUNT via efficient GROUP BY, instead of subquery in SELECT. However, even giving an exact instruction is not a guarantee that the computer will do what we told it to do, look at how stubborn Entity Framework is; though also it doesn't generate a subquery for COUNT, the approach and efficiency of Entity Framework-generated SQL is questionable and hard to reason about


A keen developer shall observe, the GROUP BY we made is not exactly the same as the subquery approach; the subquery approach could report persons without employee pay history while the INNER JOIN could not. We should do a LEFT JOIN and make a conditional count on non-null. Entity Framework solution:

var query = 
    from p in db.Set<Person>()
        .SelectMany(x => x.PayHistories.DefaultIfEmpty(), (person, payHistory) => new {person, payHistory })
    group p by new { p.person.BusinessEntityId, p.person.FirstName, p.person.LastName } into g
    select new { g.Key, Count = g.Sum(x => x.payHistory != null ? 1 : 0) };

Entity Framework-generated SQL:

SELECT
    [GroupBy1].[K1] AS [BusinessEntityId],
    [GroupBy1].[K4] AS [C1],
    [GroupBy1].[K3] AS [FirstName],
    [GroupBy1].[K2] AS [LastName],
    [GroupBy1].[A1] AS [C2]
    FROM ( SELECT
        [Join1].[K1] AS [K1],
        [Join1].[K2] AS [K2],
        [Join1].[K3] AS [K3],
        [Join1].[K4] AS [K4],
        SUM([Join1].[A1]) AS [A1]
        FROM ( SELECT
            [Extent1].[BusinessEntityId] AS [K1],
            [Extent1].[LastName] AS [K2],
            [Extent1].[FirstName] AS [K3],
            1 AS [K4],
            CASE WHEN ( NOT (([Extent2].[BusinessEntityId] IS NULL) AND ([Extent2].[RateChangeDate] IS NULL))) THEN 1 ELSE 0 END AS [A1]
            FROM  [Person].[Person] AS [Extent1]
            LEFT OUTER JOIN [HumanResources].[EmployeePayHistory] AS [Extent2] ON [Extent1].[BusinessEntityId] = [Extent2].[BusinessEntityId]
        )  AS [Join1]
        GROUP BY [K1], [K2], [K3], [K4]
    )  AS [GroupBy1]

Unfortunately, though it's a relatively easy fix on Entity Framework, we just added a DefaultIfEmpty and do a conditional count on non-null, the same won't work on NHibernate. As of the time of this writing, NHibernate Linq doesn't support DefaultIfEmpty, it can't produce a LEFT JOIN on collection nor on manual joins. NHibernate has an API for that trivial task, and its API is more complex and longer than the problem it is solving :-)

EmployeePayHistory payHistory = null;
var persons =
    session.QueryOver<Person>()
    .Left.JoinAlias(p => p.PayHistories, () => payHistory)                        
    .SelectList(x => x
        .SelectGroup(p => p.BusinessEntityId)
        .SelectGroup(p => p.FirstName)
        .SelectGroup(p => p.LastName)                            
        .SelectCount(p => payHistory.EmployeePayHistoryCompositePK.BusinessEntityId)
    )
    .List<object[]>()
    .Select(cols => new
        {
            Id = (int)cols[0],
            FirstName = (string)cols[1],
            LastName = (string)cols[2],
            Count = (int)cols[3]
        });

NHibernate-generated SQL:

SELECT
    this_.BusinessEntityId as y0_,
    this_.FirstName as y1_,
    this_.LastName as y2_,
    count(payhistory1_.BusinessEntityId) as y3_
FROM
    Person.Person this_
left outer join
    HumanResources.EmployeePayHistory payhistory1_
        on this_.BusinessEntityId=payhistory1_.BusinessEntityId
GROUP BY
    this_.BusinessEntityId,
    this_.FirstName,
    this_.LastName

With clear instructions and reasonable expectations, computers will do what you wanted it to do


Happy Coding! ツ

Lucky .NET developers

Java's signed bytes gets me every time I try to do image processing. Easy answer is "Don't do image processing in java", of course. -- John Carmack

Time to reflect on the fact that though statistically speaking we are not the lucky ones, we are lucky in terms of empowerment, we can make image processing application in C#, we can make games with it, we can make web applications as well as desktop applications with it, and we can even make an operating system with it


Happy Coding!