The .NET framework contains lots of ways to pass around data generically now. Tuples, Dynamic Type, Anonymous types, ExpandoObject, etc. But my favorite is a standard style DTO using Generic collections that I can use for business objects for paging.
For paging in an N-Tier, Repository Pattern environment, I use two different Data Transfer Objects (DTO). The first, is an object used to transfer the basic data from the data layer that contains the collection of return objects or DataRows. The second is a more detailed and flexible object that contains all the properties to satisfy 90% of my paging needs.
DataLayer PageResults
Since my service layer already knows the intimate details of my paging request, when I receive back the response from the data layer, I really only need two things:
- The collection I asked for
- The total number of items that fit my filters
I’ve always felt that if the API was made public, that less is more.
Yes, I could use the same object that I use in the service layer that has more properties, but I’ve always felt that if the API was made public, that less is more. The data layer return object is one that I call PagedResults, it’s structured like:
using System;
using System.Collections.Generic;
namespace YTG.Models
{
/// <summary>
/// Yasgar Technology Group, Inc.
/// http://www.ytgi.com
/// </summary>
/// <typeparam name="TEntity"></typeparam>
public class PagedResult<TEntity> : IPagedResult<TEntity>
{
/// <summary>
/// Primary constructor
/// </summary>
/// <param name="items"></param>
/// <param name="totalCount"></param>
public PagedResult(List<TEntity> items, int totalCount)
{
Items = items;
TotalCount = totalCount;
}
private Lazy<List<TEntity>> m_items = new Lazy<List<TEntity>>(() => new List<TEntity>(), true);
/// <summary>
/// IEnumerable list of items returned
/// Yasgar Technology Group, Inc. - www.ytgi.com
/// </summary>
public List<TEntity> Items
{
get { return m_items.Value; }
set
{
m_items = new Lazy<List<TEntity>>(() => value, true);
}
}
/// <summary>
/// Total count of records from query
/// Yasgar Technology Group, Inc. - www.ytgi.com
/// </summary>
public int TotalCount { get; set; } = 0;
}
}
You can read a little more about this object here:
Your data layer will pull back a dataset or IQueryable resultset. You can stuff that into the PagedResult with the following code:
return new PagedResult<Models.LuCategory>(_entityrows.ToList(), _totalCount);
I usually do this in a service layer before my web service front end, so something like:
- Pull back a DataSet or Entity IQueryable collection
- Return that to the service layer
- Loop through and map to a DTO and stuff into the Paging DTO
A ha! I know what you’re thinking, I would just stuff the DataSet or Entity collection in there and send it back, save some time. Right? I don’t recommend that for one main reason; you’re tying your UI to the structure of your database or ORM. I don’t want to digress in this post as to why this is not desirable, but I promise to discuss it in another post soon.
Hate writing redundant mapping code? Read this post: Stuffing DataSets into your objects.
I return this object from my system REST API or WCF web service. In my service layer in the web site, I combine the results into my UI based DTO that has the rest of the properties needed for paging, called SearchModel. It is IMPERATIVE that this DTO be based on the Interface in the project. The SearchModel object looks like this:
using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.Text.Json.Serialization;
namespace YTG.MVC.Lookups.Models
{
/// <summary>
/// View Model for Searching and holding results
/// </summary>
public class SearchModel<TEntity> : ISearchModel
{
/// <summary>
/// Default constructor
/// </summary>
public SearchModel() { }
public SearchModel(int totalItems, int? page, int pageSize = 10)
{
TotalItems = totalItems;
CurrentPage = page ?? 1;
PageSize = pageSize;
}
private int m_TotalItems = 0;
private int m_CurrentPage = 1;
private int m_PageSize = 0;
private Lazy<List<TEntity>> m_SortedResults = new Lazy<List<TEntity>>(() => new List<TEntity>(), true);
/// <summary>
/// Gets or set the total number of items to be paged
/// Yasgar Technology Group, Inc. - www.ytgi.com
/// </summary>
public int TotalItems
{
get
{ return m_TotalItems; }
set
{
m_TotalItems = value;
if (m_PageSize > 0)
{ TotalPages = (m_TotalItems + (m_PageSize - 1)) / m_PageSize; }
}
}
/// <summary>
/// Gets or sets the current page being displayed
/// Automatically populates the values of other properties
/// Yasgar Technology Group, Inc. - www.ytgi.com
/// </summary>
public int CurrentPage
{
get
{ return m_CurrentPage; }
set
{
m_CurrentPage = value < 1 ? 1 : value;
StartPage = m_CurrentPage - 5;
EndPage = m_CurrentPage + 4;
if (StartPage <= 0)
{
EndPage -= (StartPage - 1);
StartPage = 1;
}
if (EndPage > TotalPages)
{
EndPage = TotalPages;
if (EndPage > 10)
{
StartPage = EndPage - 9;
}
}
}
}
/// <summary>
/// Gets or sets the page size currently set
/// Yasgar Technology Group, Inc. - www.ytgi.com
/// </summary>
public int PageSize
{
get
{ return m_PageSize; }
set
{
m_PageSize = value;
if (m_TotalItems > 0)
{ TotalPages = (m_TotalItems + (m_PageSize - 1)) / m_PageSize; }
// To get EndPage set correctly if this property is set last
CurrentPage = m_CurrentPage;
}
}
/// <summary>
/// Gets or set the total number of pages based on the TotalItems and PageSize
/// Yasgar Technology Group, Inc. - www.ytgi.com
/// </summary>
public int TotalPages { get; set; } = 0;
/// <summary>
/// Gets or sets the start page for the pager display
/// Yasgar Technology Group, Inc. - www.ytgi.com
/// </summary>
public int StartPage { get; set; } = 0;
/// <summary>
/// Gets or sets the end page for the pager display
/// Yasgar Technology Group, Inc. - www.ytgi.com
/// </summary>
public int EndPage { get; set; } = 0;
/// <summary>
/// Gets or sets the search filter for the paged items
/// Yasgar Technology Group, Inc. - www.ytgi.com
/// </summary>
public string SearchFilter { get; set; } = string.Empty;
/// <summary>
/// Gets or sets the search term for the paged items
/// Yasgar Technology Group, Inc. - www.ytgi.com
/// </summary>
public string SearchTerm { get; set; } = string.Empty;
/// <summary>
/// Gets or sets the sort expression for the paged items
/// Yasgar Technology Group, Inc. - www.ytgi.com
/// </summary>
public string SortColumn { get; set; } = string.Empty;
/// <summary>
/// Gets or sets the previous sort expression for the paged items when posting back to controller
/// Yasgar Technology Group, Inc. - www.ytgi.com
/// </summary>
public string PrevSortColumn { get; set; } = string.Empty;
/// <summary>
/// Gets or sets the count of records in the current page
/// Yasgar Technology Group, Inc. - www.ytgi.com
/// </summary>
public int RecordCount { get; set; } = 0;
/// <summary>
/// Gets or sets the sort order, default is asc
/// Yasgar Technology Group, Inc. - www.ytgi.com
/// </summary>
public bool SortDescending { get; set; } = false;
/// <summary>
/// Gets or sets whether the paged items only contain active records
/// Yasgar Technology Group, Inc. - www.ytgi.com
/// </summary>
[Display(Name = "Active Only")]
public bool ActiveOnly { get; set; } = true;
/// <summary>
/// Gets or sets the Reference Id, to be used for a parent object
/// Yasgar Technology Group, Inc. - www.ytgi.com
/// </summary>
public long RefId { get; set; } = 0;
/// <summary>
/// Gets or sets the Reference Unique Id, to be used for a parent object
/// Yasgar Technology Group, Inc. - www.ytgi.com
/// </summary>
public Guid RefUniqueId { get; set; } = Guid.Empty;
/// <summary>
/// Gets or sets the List of pre-sorted results
/// Yasgar Technology Group, Inc. - www.ytgi.com
/// </summary>
public List<TEntity> SortedResults
{
get { return m_SortedResults.Value; }
set
{
m_SortedResults = new Lazy<List<TEntity>>(() => value, true);
}
}
/// <summary>
/// Gets or sets the controller name for this Model
/// Needed for Pagination partial views
/// Yasgar Technology Group, Inc. - www.ytgi.com
/// </summary>
public string controllerName { get; set; } = string.Empty;
/// <summary>
/// Gets or sets the action name for this model
/// Needed for Pagination partial views
/// Yasgar Technology Group, Inc. - www.ytgi.com
/// </summary>
public string actionName { get; set; } = string.Empty;
}
}
I use the simpler PagedResults to return the data collection and the total count from my repository. Then push this data, combined with whatever filter options were sent in back to the View.
You can take a look at how these objects are used in my sample app on GitHub:
https://github.com/YTGI/YTG-MVC-Lookups