I'm looking to implement a few nicer ways to use List in a couple of apps I'm working on. My current implementation looks like this.
MyPage.aspx.cs
protected void Page_Load(object sender, EventArgs e)
{
BLL.PostCollection oPost = new BLL.PostCollection();
oPost.OpenRecent();
rptPosts.DataSource = oArt;
rptPosts.DataBind();
}
BLL Class(s)
public class Post
{
public int PostId { get; set; }
public string PostTitle { get; set; }
public string PostContent { get; set; }
public string PostCreatedDate { get; set; }
public void OpenRecentInitFromRow(DataRow row)
{
this.PostId = (int) row["id"];
this.PostTitle = (string) row["title"];
this.PostContent = (string) row["content"];
this.PostCreatedDate = (DateTime) row["createddate"];
}
}
public class PostCollection : List<Post>
{
public void OpenRecent()
{
DataSet ds = DbProvider.Instance().Post_ListRecent();
foreach (DataRow row in ds.Tables[0].Rows)
{
Post oPost = new Post();
oPost.OpenRecentInitFromRow(row);
Add(oPost);
}
}
}
Now while this is working all well and good, I'm just wondering if there is any way to improve it, and just make it cleaner that having to use the two different classes do to something I think can happen in just one class or using an interface.
For one thing, I wouldn't derive from List<T> - you aren't really specializing the behaviour.
I'd also suggest that you could make Post immutable (at least externally), and write a static method (or constructor) to create one based on a DataRow:
public static Post FromDataRow(DataRow row)
Likewise you can have a list method:
public static List<Post> RecentPosts()
which returns them. Admittedly that might be better as an instance method in some sort of DAL class, which will allow mocking etc. Alternatively, in Post:
public static List<Post> ListFromDataSet(DataSet ds)
Now, as for the use of List<T> itself - are you using .NET 3.5? If so, you could make this considerably neater using LINQ:
public static List<Post> ListFromDataSet(DataSet ds)
{
return ds.Tables[0].AsEnumerable()
.Select(row => Post.FromDataRow(row))
.ToList();
}
Are you deriving from List<T> because you want to offer other consumers of PostCollection the ability to Add and Remove items? I'm guessing not, and that you actually just want a way to expose a collection you can bind to. If so, you could consider an iterator, perhaps:
class BLL {
...
public IEnumerable<Post> RecentPosts {
get {
DataSet ds = DbProvider.Instance().Post_ListRecent();
foreach (DataRow row in ds.Tables[0].Rows)
{
Post oPost = new Post();
oPost.OpenRecentInitFromRow(row);
yield return oPost;
}
}
}
...
}
Notwithstanding the fact that this might be considered poor form (in that we have a property getter that might be making a network call), this iterator approach will do away with the overhead of calling OpenRecentInitFromRow for Posts that are never enumerated.
You also become agnostic as to how potential consumers of your Posts might want to consume them. Code that absolutely, positively has to have every Post can do ToList(), but other code might want to use a LINQ query that short-circuits the enumeration after the right Post is found.
Edit: John Skeet's answer is probably a better option. But if you want to make just a few simple changes, read on:
Place the database access code, OpenRecentInitFromRow into the PostCollection and treat that as a Post manager class. That way the Post class is a plain old Data Transfer Object.
public class Post
{
public int PostId { get; set; }
public string PostTitle { get; set; }
public string PostContent { get; set; }
public string PostCreatedDate { get; set; }
}
public class PostCollection : List<Post>
{
public void OpenRecent()
{
DataSet ds = DbProvider.Instance().Post_ListRecent();
foreach (DataRow row in ds.Tables[0].Rows)
{
Add(LoadPostFromRow(row));
}
}
private Post LoadPostFromRow(DataRow row)
{
Post post = new Post();
post.PostId = (int) row["id"];
post.PostTitle = (string) row["title"];
post.PostContent = (string) row["content"];
post.PostCreatedDate = (DateTime) row["createddate"];
return post;
}
}
I'm looking to implement a few nicer ways to use List
That seems like an odd request. The "List" type is a means, rarely an end. With that in mind, one nicer way to accomplish your real end is to use IEnumerable rather than List, because that List forces you to keep your entire collection in memory while IEnumerable only requires one object at a time. The trick is just that you have to wire everything in your processing stream, from the data layer all the way up through presentation, to use it.
I have a good example in the link below about how to do this in a very clean way:
Fastest method for SQL Server inserts, updates, selects
Depending on your existing data layer code you may be able to skim much of the first half of the (long) post - the main point is that you use an iterator block to turn an SqlDataReader into an IEnumerable<IDataRecord>. Once you have that, it's pretty straightforward the rest of the way through.
You could do this:
protected void Page_Load(object sender, EventArgs e)
{
BLL.PostCollection oPost = new BLL.PostCollection();
rptPosts.DataSource = Post.OpenRecent();
rptPosts.DataBind();
}
public class Post
{
public int PostId { get; set; }
public string PostTitle { get; set; }
public string PostContent { get; set; }
public string PostCreatedDate { get; set; }
public void OpenRecentInitFromRow(DataRow row)
{
this.PostId = (int) row["id"];
this.PostTitle = (string) row["title"];
this.PostContent = (string) row["content"];
this.PostCreatedDate = (DateTime) row["createddate"];
}
public static List<Post> OpenRecent()
{
DataSet ds = DbProvider.Instance().Post_ListRecent();
foreach (DataRow row in ds.Tables[0].Rows)
{
Post oPost = new Post();
oPost.OpenRecentInitFromRow(row);
Add(oPost); //Not sure what this is doing
}
//need to return a List<Post>
}
}
Related
I am learning DDD and trying to model articles, its variants and parameters.
Article can be on it's own without variants
Variant must be child of an article
both article and variant can have some parameters (colors, brands, sizes...), physical quantities (width, length, some article-specific like inner length)
If you set some parameter on an article, it can be "synchronized" to it's children variants
you can override this in a variant by setting that parameter as "unlinked", then this variant would have different parameter value than article
some parameters can be set multiple times (color: red, blue), but some only once (brand)
those parameters are dynamically create, it's not a Color or Brand property but key-value selected from preconfigured values
I think my main aggregate roots will be Article and Variant.
My current code looks like this:
internal class Article : AggregateRoot<ArticleId>
{
private readonly ISet<VariantId> _variants = new HashSet<VariantId>();
private readonly ISet<AssignedParameter> _parameters = new HashSet<AssignedParameter>();
private readonly ISet<AssignedPhysicalQuantity> _physicalQuantities = new HashSet<AssignedPhysicalQuantity>();
public string Name { get; private set; }
public string Catalog { get; private set; }
public IReadOnlySet<VariantId> Variants => _variants.AsReadOnly();
public IReadOnlySet<AssignedParameter> Parameters => _parameters.AsReadOnly();
public IReadOnlySet<AssignedPhysicalQuantity> PhysicalQuantities => _physicalQuantities.AsReadOnly();
private Article(ArticleId id, string name, string catalog)
: base(id)
{
Name = name;
Catalog = catalog;
}
public static Article Register(ArticleId id, string name, string catalog)
{
var article = new Article(id, name, catalog);
article.AddEvent(new ArticleRegistered(article.Id, article.Name, article.Catalog));
return article;
}
public void AssignParameter(Parameter parameter, ParameterValue parameterValue, bool syncToVariants)
{
if (!parameter.CanBeAssignedMultipleTimes && _parameters.Any(p => p.ParameterId == parameter.Id))
{
throw new ParameterCanBeAssignedOnlyOnceException($"Parameter {parameter.Id} can by assigned only once.");
}
var assignedParameter = new AssignedParameter(parameter.Id, parameterValue.Id, syncToVariants);
if (!_parameters.Add(assignedParameter))
{
throw new ParameterIsAlreadyAssignedException($"Parameter {parameter.Id} with value {parameterValue.Id} is already assigned.");
}
AddEvent(new ArticleParameterAssigned(Id, assignedParameter.ParameterId, assignedParameter.ParameterValueId));
}
public void UnassignParameter(Parameter parameter, ParameterValue parameterValue)
{
var assignedParameter = _parameters.FirstOrDefault(p => p.ParameterId == parameter.Id && p.ParameterValueId == parameterValue.Id);
if (assignedParameter is null)
{
throw new ParameterIsNotAssignedException($"Parameter {parameter.Id} is not assigned.");
}
_parameters.Remove(assignedParameter);
AddEvent(new ArticleParameterUnassigned(Id, assignedParameter.ParameterId, assignedParameter.ParameterValueId));
}
// physical quantity assign / unassign are similar to parameters
}
internal class Variant : AggregateRoot<VariantId>
{
private readonly ISet<AssignedParameter> _parameters = new HashSet<AssignedParameter>();
private readonly ISet<AssignedPhysicalQuantity> _physicalQuantities = new HashSet<AssignedPhysicalQuantity>();
public string Name { get; private set; }
public string Catalog { get; private set; }
public EanCode Ean { get; private set; }
public decimal Weight { get; private set; }
public IReadOnlySet<AssignedParameter> Parameters => _parameters.AsReadOnly();
public IReadOnlySet<AssignedPhysicalQuantity> PhysicalQuantities => _physicalQuantities.AsReadOnly();
internal Variant(VariantId id, string name, string catalog, EanCode ean, decimal weight)
: base(id)
{
Name = name;
Catalog = catalog;
Ean = ean;
Weight = weight;
}
// parameter and physical quantity assignment methods
}
Parameters:
internal class Parameter : AggregateRoot<ParameterId>
{
private readonly ISet<ParameterValue> _values = new HashSet<ParameterValue>();
public string Code { get; private set; }
public string Name { get; private set; }
public bool CanBeAssignedMultipleTimes { get; private set; }
public IReadOnlySet<ParameterValue> Values => _values.AsReadOnly();
public Parameter(ParameterId id, string code, string name, bool canBeAssignedMultipleTimes)
: base(id)
{
Code = code;
Name = name;
CanBeAssignedMultipleTimes = canBeAssignedMultipleTimes;
}
}
internal class ParameterValue : Entity<ParameterValueId>
{
public string Code { get; private set; }
public string Name { get; private set; }
public Parameter Parameter { get; private init; } = null!;
public ParameterValue(ParameterValueId id, string code, string name)
: base(id)
{
Code = code;
Name = name;
}
}
Value objects:
// for Article, variant doesn't have SyncToVariants property and has some other
internal class AssignedParameter : ValueObject
{
public ParameterId ParameterId { get; private init; }
public ParameterValueId ParameterValueId { get; private init; }
public bool SyncToVariants { get; private init; }
public AssignedParameter(ParameterId parameterId, ParameterValueId parameterValueId, bool syncToVariants)
{
ParameterId = parameterId;
ParameterValueId = parameterValueId;
SyncToVariants = syncToVariants;
}
protected override IEnumerable<object> GetEqualityComponents()
{
yield return ParameterId;
yield return ParameterValueId;
}
}
internal class AssignedPhysicalQuantity : ValueObject { ... }
My questions:
What would be the best way to notify variants of the parameter change? I can think of two ways using events.
First would be using ArticleParameterChanged(ArticleId, parameter.Id, parameterValue.Id). I would handle this event and changed all variants at once in the handler - I don't think this is the way, but I wouldn't need to hold variants collection in article.
Second would be to loop through variant IDs and create ArticleVariantParameterChanged(ArticleId, VariantId, parameterId, parameterValueId) event. This seems more correct to me?
if (syncToVariants)
{
foreach (var variantId in _variants)
{
AddEvent(new ArticleVariantParameterChanged(Id, variantId, parameter.Id, parameterValue.Id);
}
}
How do I add new variant to article? The easiest way would be to create new variant and update the article in one transaction.
// Article method
public Variant RegisterVariant(VariantId variantId, ...)
{
var variant = new Variant(variantId, ...);
_variants.Add(variantId);
return variant;
}
// command handler? or domain service?
var article = await _articleRepo.GetAsync(articleId);
var variant = article.RegisterVariant(variantId, ...);
await _variantRepo.AddAsync(variant);
await _articleRepo.UpdateAsync(article);
Or using events?
// Article method
public Variant RegisterVariant(VariantId variantId, ...)
{
var variant = Variant.Register(variantId, this.Id, ...);
return variant;
}
// Variant static method
public Variant Register(VariantId variantId, ArticleId articleId, ...)
{
var variant = new Variant(variantId, articleId, ...);
variant.AddEvent(new VariantRegistered(variantId, articleId));
return variant;
}
// command handler
var variant = article.RegisterVariant(...);
await _variantRepo.AddAsync(variant);
// VariantRegisteredHandler
article.AddVariant(variantId);
However here it seems kind of confusing to me, article.RegisterVariant and article.AddVariant... Maybe it's just wrong naming?
Also here can occur condition race between adding new variant and assigning a new parameter, when someone adds new parameter before the VariantRegistered event was handled, so it wouldn't sync that parameter.
So I'm thinking, is it even good idea to store those shared parameters in each variant? Maybe it would be enough to just have variant specific parameters there and merge everything in the read model? However this would be harder to prevent duplications - if the article already has a parameter "color - red", assigning "color - red" to variant would need to check the article parameters too and there can be another race condition.
I read that entities without any domain business logic could be treated as CRUD, that means they wouldn't even inherit AggregateRoot and each of them would have own repository, right?
Let's say someone really wants to delete some parameter value, for example blue color. This wouldn't (hopefully) happen in my app, but I'm still curious how this would be handled. He confirms he really wants to delete it and I need to go through all articles and unassign it from them. How?
My idea would be either to have ParameterValueDeleted event and ParameterValueDeletedHandler would query for all articles and variants and unassign it one by one, this handler would take really long time to execute.
Or ParameterValueDeletedHandler would query for all IDs, create some event for them and that handler would unassign it later. However in the latter case I don't know how that event would be named to make sense. UnassignArticleParameter seems more like command than event and ArticleParameterUnassigned is something coming from article. Also I read that commands indicate something that can be rejected, so I would say command doesn't fit here.
Also I see a problem when someone deletes that parameter and someone else queries for an article which doesn't have it unassigned yet - database join would fail because it would join to non existent parameter (considering single database for read and write model).
If I wanted to have mandatory parameters, where would be the best place to validate that all of them are set? Move the article registration logic to ArticleFactory and check it there? And for variants maybe ArticleService or VariantFactory? This seems kinda inconsistent to me, but maybe it's right?
var article = await _articleRepo.GetAsync(articleId);
_articleService.RegisterVariant(article, /* variant creation data */);
_variantFactory.Register(article, /* variant creation data */);
I think this should be all, I hope I explained everything well.
I would appreciate any help with this!
I have classes that I use with EntityFramework:
public partial class BaseDocument
{
public BaseDocument()
{
DocumentLinks = new List<DocumentLink>();
}
public int Id {set;get;}
public virtual List<DocumentLink> DocumentLinks {set;get;}
}
public partial class Payment:BaseDocument
{
}
public partial class Bill:BaseDocument
{
}
public partial class DocumentLink
{
public int Id{set;get;}
public int StartDocId{set;get;}
public int EndDocId{set;get;}
public virtual BaseDocument StartDoc{set;get;}
public virtual BaseDocument EndDoc{set;get;}
}
Now I select document with Linq and want to iterate through list of his DocumentLinks.
var payment = dbContext.Payments.First(t=>t.Id = id);
foreach(var link in payment.DocumentLinks)
{
if (link is Payment)
{
//do something
}
else if (link is Bill)
{
//do something
}
}
And my code works very slowly at the line if (link is Payment). After this line everything works quickly.
What is wrong?
You mean it is slow in the line that is actually executing the database query? Hint - this is why it is slow.
var payment = dbContext.Payments.First(t=>t.Id = id);
I fail to see how the payment includes the DocumentLiks - which means they are lazy loaded. Which means this happens in the foreach. And there you go. Slow.
Include them in the initial query.
Not a direct answer to your question, but a suggestion that you shouldn't type-sniff like this. Polymorphism allows you to ignore the exact type of an object, use it.
Put whatever behavior you need into BaseDocument and remove the is Payment and is Bill:
var payment = dbContext.Payments[id];
foreach(var link in payment.DocumentLiks)
{
link.DoSomething();
}
This may be because of Lazy loading.
In your DBContext configuration specify:
this.Configuration.LazyLoadingEnabled = false;
I have a little design problem. Let's say I have a project that contains a large number of people. I want to allow the user to export those people to a CSV file with the information he chooses.
For example, He could choose Id, Name, Phone number and according to his choice I would create the file.
Of course, there is a simple of way doing it like if(idCheckBox.Checked) getId(); etc.
I'm looking for something better. I don't want that for each new option I would like to add I would need to change the UI (e.g. New checkbox).
I thought of reading the possible options from a file, but that will only solved the UI problem. How would I know which values to get without using all those "if's" again?
You don't need a fancy design pattern for this task. However I understand you have identified a reason to change (added options in future). So you want to minimize amount of classes to be modified.
Your real problem is how to decouple CSV creation from the objects whose structure is going to change. You don't want your parsing logic to be affected whenever your Person class is changed.
In the following example the CSV object is truly decoupled from the objects it receives and parses. To achieve this, we are coding to an abstraction rather to an implementation. This way we are not even coupled to the Person object, but will welcome any objects that implement the AttributedObject interface. This dependency is being injected to our CSV parser.
I implemented this in PHP, but the idea is the same. C# is a static language, so fetching the attributes would be with a bit of change. You might use some kind of ArrayAccess interface.
interface AttributedObject {
public function getAttribute($attribute);
}
class Person implements AttributedObject {
protected $firstName;
protected $lastName;
protected $age;
protected $IQ;
public function __construct($firstName, $lastName, $age, $IQ)
{
$this->firstName = $firstName;
$this->lastName = $lastName;
$this->age = $age;
$this->IQ = $IQ;
}
public function getAttribute($attribute)
{
if(property_exists($this, $attribute)) {
return $this->$attribute;
}
throw new \Exception("Invalid attribute");
}
}
class CSV {
protected $attributedObject = null;
protected $attributesToDisplay = null;
protected $csvRepresentation = null;
protected $delimiter = null;
public function __construct(AttributedObject $attributedObject, array $attributesToDisplay, $delimiter = '|')
{
$this->attributedObject = $attributedObject;
$this->attributesToDisplay = $attributesToDisplay;
$this->delimiter = $delimiter;
$this->generateCSV();
}
protected function generateCSV()
{
$tempCSV = null;
foreach ($this->attributesToDisplay as $attribute) {
$tempCSV[] = $this->attributedObject->getAttribute($attribute);
}
$this->csvRepresentation = $tempCSV;
}
public function storeCSV()
{
$file = fopen("tmp.csv", "w");
fputcsv($file, $this->csvRepresentation, $this->delimiter);
}
}
$person1 = new Person('John', 'Doe', 30, 0);
$csv = new CSV($person1, array('firstName', 'age', 'IQ'));
$csv->storeCSV();
You can build a mapping set of fields based what fields the user is allowed to select, and which fields are required. This data can be read from a file or database. Your import/export can be as flexible as needed.
Here is a conceivable data structure that could hold info for your import/export sets.
public class FieldDefinition
{
public FieldDataTypeEnum DataType { get; set; }
public string FieldName{get;set;}
public int MaxSize { get; set; }
public bool Required { get; set; }
public bool AllowNull { get; set; }
public int FieldIndex { get; set; }
public bool CompositeKey { get; set; }
}
public class BaseImportSet
{
private List<FieldDefinition> FieldDefinitions { get; set; }
protected virtual void PerformImportRecord(Fields selectedfields)
{
throw new ConfigurationException("Import set is not properly configured to import record.");
}
protected virtual void PerformExportRecord(Fields selectedfields)
{
throw new ConfigurationException("Export set is not properly configured to import record.");
}
public LoadFieldDefinitionsFromFile(string filename)
{
//Implement reading from file
}
}
public class UserImportSet : BaseImportSet
{
public override void PerformImportRecord(Fields selectedfields)
{
//read in data one record at a time based on a loop in base class
}
public override string PerformExportRecord(Fields selectedfields)
{
//read out data one record at a time based on a loop in base class
}
}
I am using Domain Service to fetch data from database from Silverlight Client.
In DomainService1.cs, I have added the following:
[EnableClientAccess()]
public class Product
{
public int productID;
public string productName;
public List<Part> Parts = new List<Part>(); //Part is already present in Model designer
}
In DomainService1 class I added a new method to retrive a collection of the custom class object:
[EnableClientAccess()]
public class DomainService1 : LinqToEntitiesDomainService<HELPERDBNEWEntities1>
{
...
public List<Product> GetProductsList(...)
{
List<Product> resultProducts = new List<Product>();
...
return resultProducts;
}
}
From the silverlight client I am trying to access that method:
DomainService1 ds1 = new DomainService1();
var allproductList = ds1.GetProductsList(...);
ds1.Load<SLProduct>(allproductList).Completed += new EventHandler(Load_Completed); //Not correct usage
However it is not the correct way to call the new method. The reason I added a new class Product in DomainServices.cs is to have an efficient grouping. I cannot achieve the same using the model classes auto-generated by the entity framework.
How call I call the new method from the client?
I believe there is a similar question with an answer here:
Can a DomainService return a single custom type?
Also, here is some discussion about the overall problem of adding custom methods in a Domain Service:
http://forums.silverlight.net/t/159292.aspx/1
While I don't know what you mean by "it is not the correct way to call the new method", or if you're getting any errors, I thought maybe posting some working code might help.
My POCO
public class GraphPointWithMeta
{
[Key]
public Guid PK { get; set; }
public string SeriesName { get; set; }
public string EntityName { get; set; }
public double Amount { get; set; }
public GraphPointWithMeta(string seriesName, string entityName, double amount)
{
PK = Guid.NewGuid();
SeriesName = seriesName;
EntityName = entityName;
Amount = amount;
}
// Default ctor required.
public GraphPointWithMeta()
{
PK = Guid.NewGuid();
}
}
A method in the domain service (EnableClientAccess decorates the class)
public IEnumerable<GraphPointWithMeta> CallingActivityByCommercial()
{
List<GraphPointWithMeta> gps = new List<GraphPointWithMeta>();
// ...
return gps;
}
Called from the Silverlight client like
ctx1.Load(ctx1.CallingActivityByCommercialQuery(), CallingActivityCompleted, null);
client call back method
private void CallingActivityCompleted(LoadOperation<GraphPointWithMeta> lo)
{
// lo.Entities is an IEnumerable<GraphPointWithMeta>
}
I am not sure if your Product class is an actual entity or not. From the way it is defined, it does not appear to be an entity. My answer is assuming it is not an entity. You will need to apply the DataMemberAttribute for your Product properties, and you wouldn't load the product list - load is for Entity Queries (IQueryable on the service side). You would just invoke it like this (client side):
void GetProductList( Action<InvokeOperation<List<Product>>> callback)
{
DomainService ds1 = new DomainService();
ds1.GetProductsList(callback, null);//invoke operation call
}
And the domain service's (server side) method needs the InvokeAttribute and would look like this:
[EnableClientAccess]
public class MyDomainService
{
[Invoke]
public List<Product> GetProductList()
{
var list = new List<Product>();
...
return list;
}
}
And here is how your Product class might be defined (if it is not an entity):
public class Product
{
[DataMember]
public int productID;
[DataMember]
public string productName;
[DataMember]
public List<Part> Parts = new List<Part>(); // you might have some trouble here.
//not sure if any other attributes are needed for Parts,
//since you said this is an entity; also not sure if you
//can even have a list of entities or it needs to be an
//entity collection or what it needs to be. You might
//have to make two separate calls - one to get the products
//and then one to get the parts.
}
Like I said, i am not sure what Product inherits from... Hope this helps.
I was looking to map my database query results to strongly type objects in my c# code. So i wrote a quick and dirty helper method on the SqlConnection class which runs the query on the database and uses reflection to map the record columns to the object properties. The code is below:
public static T Query<T>(this SqlConnection conn, string query) where T : new()
{
T obj = default(T);
using (SqlCommand command = new SqlCommand(query, conn))
{
using (SqlDataReader reader = command.ExecuteReader())
{
while (reader.Read())
{
obj = new T();
PropertyInfo[] propertyInfos;
propertyInfos = typeof(T).GetProperties();
for (int i = 0; i < reader.FieldCount; i++)
{
var name = reader.GetName(i);
foreach (var item in propertyInfos)
{
if (item.Name.Equals(name, StringComparison.InvariantCultureIgnoreCase) && item.CanWrite)
{
item.SetValue(obj, reader[i], null);
}
}
}
}
}
}
return obj;
}
public class User
{
public int id { get; set; }
public string firstname { get; set; }
public string lastname { get; set; }
public DateTime signupDate { get; set; }
public int age { get; set; }
public string gender { get; set; }
}
var user = conn.Query<User>("select id,firstname,lastname from users");
I just wanted a second opinion on my approach above of using reflection to tie the values together, if there's anything i can do better in the code above. Or if there's some other totally different approach i can take to get the same result?
I think i can probably improve the code in the helper method by removing the loop for propertyInfos and using a dictionary instead. Is there anything else that needs to be tweaked?
P.S: i'm aware of Dapper, i just wanted to implement something similar on my own to help me learn better.
What you've done is basically what linq-to-sql or other OR-mappers do under the hood. To learn the details of how it works it's always a good idea to write something from scratch.
If you want more inspiration or want to have something that's ready for production use out-of-the-box I'd recommend reading up on linq-to-sql. It is lightweight, yet competent.
There are a few of things I can think of:
I think that in order to skip the loop you can use:
reader[item.Name]
I've done something similar myself, but I never ran into dapper. I'm not sure if it uses reflection, but it's always a good idea to read someone else's code to sharpen your skill (Scott Hanselman frequently recommends doing so).
You can also look at:
http://www.codeproject.com/KB/database/metaquery_part1.aspx
You can implement an attribute that maps a field to a database column, but that's just for fun.
Edit:
5: You can also skip the while loop over the reader and just take the first row, and document the fact that your query only returns one object, so it doesn't pull a thousand rows if the query returns a thousand rows.