I'm just discovering LINQ and finding it great. One problem thoush is that I have to copy a lot of fields during an update in a 3-tier (layer) application. The algorithm I used shows a typical LINQ update of a class.
I receive the object FromPresentation from the presentation layer.
I use LINQ to get the object with the same ID from the database.
I change a lot of fields
Save the changes.
And the corresponding code:
using (var ctx = new AppDataDataContext())
{
var OBJ =
(from Usu in ctx.usuarios
where Usu.ID == FromPresentation.ID
select Usu).SingleOrDefault();
if (OBJ != null)
{
OBJ.Nome = FromPresentation.Nome;
OBJ.NomeCurto = FromPresentation.NomeCurto;
OBJ.Login = FromPresentation.Login;
OBJ.Senha = FromPresentation.Senha;
OBJ.SuperUsuario = FromPresentation.SuperUsuario;
OBJ.Ativo = FromPresentation.Ativo;
// a lot more fields
ctx.SubmitChanges();
return OBJ.ID;
}
}
The problem is that I have a lot of fields. I even tried using reflection (using this question for guidance) to copy the fields but LINQ is not notified of the changes so it doesn't save anything.
How can I use reflection to copy values to a LINQ object so it can be updated in the database?
Don't use reflection for this, that would be reinventing the wheel - use a mapper like AutoMapper to do the work for you.
AutoMapper uses a fluent configuration API to define an object-object
mapping strategy. AutoMapper uses a convention-based matching
algorithm to match up source to destination values. Currently,
AutoMapper is geared towards model projection scenarios to flatten
complex object models to DTOs and other simple objects, whose design
is better suited for serialization, communication, messaging, or
simply an anti-corruption layer between the domain and application
layer.
You could try updating the properties rather than the fields.
eg
private static void UpdateForType(Type type, MyObject source, MyObject destination)
{
var myObjectProperties = type.GetProperties(
BindingFlags.NonPublic | BindingFlags.Public | BindingFlags.Instance);
foreach (PropertyInfo pi in myObjectProperties)
pi.SetValue(destination, pi.GetValue(source, null), null);
}
Related
I wrote a simple recursive function to climb up the tree of a table that has ID and PARENTID.
But when I do that I get this error
System.InvalidOperationException: 'The instance of entity type 'InternalOrg' cannot be tracked because another instance with the same key value for {'Id'} is already being tracked. When attaching existing entities, ensure that only one entity instance with a given key value is attached.
Is there another way to do this or maybe done in one LINQ expression ?
private InternalOrgDto GetInternalOrgDto(DepartmentChildDto dcDto)
{
if (dcDto.InternalOrgId != null)
{
InternalOrg io = _internalOrgRepo.Get(Convert.ToInt32(dcDto.InternalOrgId));
InternalOrgDto ioDto = new InternalOrgDto
{
Id = io.Id,
Abbreviation = io.Abbreviation,
Code = io.Code,
Description = io.Description
};
return ioDto;
}
else
{
//manually get parent department
Department parentDepartment = _departmentRepo.Get(Convert.ToInt32(dcDto.ParentDepartmentId));
DepartmentChildDto parentDepartmenDto = ObjectMapper.Map<DepartmentChildDto>(parentDepartment);
return GetInternalOrgDto(parentDepartmenDto);
}
}
Is there a way to get a top-level parent from a given child via Linq? Not that I am aware of. You can do it recursively similar to what you have done, though I would recommend simplifying the query to avoid loading entire entities until you get what you want. I'm guessing from your code that only top level parent departments would have an InternalOrg? Otherwise this method would recurse up the parents until it found one. This could be sped up a bit like:
private InternalOrgDto GetInternalOrgDto(DepartmentChildDto dcDto)
{
var internalOrgid = dcDto.InternalOrgId
?? FindInternalOrgid(dcDto.ParentDepartmentId)
?? throw new InternalOrgNotFoundException();
InternalOrgDto ioDto = _context.InternalOrganizations
.Where(x => x.InternalOrgId == internalOrgId.Value)
.Select(x => new InternalOrgDto
{
Id = x.Id,
Abbreviation = x.Abbreviation,
Code = x.Code,
Description = x.Description
}).Single();
return ioDto;
}
private int? FindInternalOrgid(int? departmentId)
{
if (!departmentId.HasValue)
return (int?) null;
var details = _context.Departments
.Where(x => x.DepartmentId == departmentId.Value)
.Select(x => new
{
x.InternalOrgId,
x.ParentDepartmentId
}).Single();
if (details.InternalOrgId.HasValue)
return details.InternalOrgId;
return findInternalOrgId(details.parentDepartmentId);
}
The key considerations here are to avoid repository methods that return entities or sets of entities, especially where you don't need everything about an entity. By leveraging the IQueryable provided by EF through Linq we can project down to just the data we need rather than returning every field. The database server can accommodate this better via indexing and help avoid things like locks. If you are using repositories to enforce low level domain rules or to enable unit testing then the repositories can expose IQueryable<TEntity> rather than IEnumerable<TEntity> or even TEntity to enable projection and other EF Linq goodness.
Another option to consider where I have hierarchal data where the relationships are important and I want to quickly find all related entities to a parent, or get to a specific level, one option is to store a breadcrumb with each record which is updated if that item is ever moved. The benefit is that these kinds of checks become very trivial to do, the risk is that anywhere/anything that can modify data relationships could leave the breadcrumb trail in an invalid state.
For example, if I have a Department ID 22 which belongs to Department 8 which belongs to Department 2 which is a top-level department, 22's breadcrumb trail would be: "2,8". If the breadcrumbs are empty we have a top-level entity. (and no parent Id) We can parse the breadcrumbs using a simple string.Split() operation. This avoids the recursive trips to the DB entirely. Though you may want a maintenance job running behind the scenes to periodically inspect recently modified data to ensure their breadcrumb trails are accurate and alerting you if any get broken. (Either by faulty code or such)
I am working on a MVC3 application with nhibernate and SQL server. Have written a normal method which is re-usable. Please find the below code and let me know a better way to handle it. I have observed to execute this piece of code it is taking a long time.
private void GetParentCompany(IEnumerable<Company> companiesList)
{
foreach (var company in companiesList)
{
long? dunsUltimateParent = company.DUNSUltimateParent;
Company ultimateParent = _companyService.GetCompanyByDUNS(Convert.ToInt64(dunsUltimateParent));
if (ultimateParent != null)
{
company.UltimateParentName = ultimateParent.CompanyName;
company.UltimateCompanyId = ultimateParent.CompanyId;
company.UltimateParentDuns = ultimateParent.DUNS;
}
}
}
Adding an index to your company.DUNS column might help. However consider to introduce a many-to-one relationship from company to (parent) company.
Place a UltimateParent property with type company in the company class. The fields UltimateParentName and UltimateParentDuns would then be redundant and you could simply get company.UltimateParent.Name for example. The mapping of UltimateParent can be done using 'References' in fluent-nhibernate.
References(x => x.UltimateParent);
I am developing an ASP.NET MVC3 application in C#.
I am trying to implement in my application a "narrow-down" functionality applied the result-set obtained from a search.
In short, after I perform a search and the results displayed in the center of the page, I would like to have on the left/right side of the page a CheckBoxList helper for each property of the search result. The CheckBox of each CheckBoxList represent the distinct values of the property.
For instance if I search Product and it has a Color property with values blue, red and yellow, I create a CheckBoxList with text Color and three CheckBox-es one for each color.
After a research on the Web I found this Dynamic LINQ library made available by Scott Guthrie. Since the most recent example/tutorial I found is from 2009, I was wondering whether this library is actually good (and maintained) or not.
In the latter case is jQuery the best way to implement such functionality?
You can solve it by building the needed predicate expressions dynamically, using purely .NET framework.
See code sample below. Depending on the criteria, this will filter on multiple properties. I've used IQuerable because this will enable both In-Memory as remote scenario's such as Entity Framework. If you're going with Entity Framework, you could also just build an EntitySQL string dynamically. I expect that will perform better.
There is a small portion of reflection involved (GetProperty). But this could be improved by performing caching inside the BuildPredicate method.
public class Item
{
public string Color { get; set; }
public int Value { get; set; }
public string Category { get; set; }
}
class Program
{
static void Main(string[] args)
{
var list = new List<Item>()
{
new Item (){ Category = "Big", Color = "Blue", Value = 5 },
new Item (){ Category = "Small", Color = "Red", Value = 5 },
new Item (){ Category = "Big", Color = "Green", Value = 6 },
};
var criteria = new Dictionary<string, object>();
criteria["Category"] = "Big";
criteria["Value"] = 5;
var query = DoDynamicWhere(list.AsQueryable(), criteria);
var result = query.ToList();
}
static IQueryable<T> DoDynamicWhere<T>(IQueryable<T> list, Dictionary<string, object> criteria)
{
var temp = list;
//create a predicate for each supplied criterium and filter on it.
foreach (var key in criteria.Keys)
{
temp = temp.Where(BuildPredicate<T>(key, criteria[key]));
}
return temp;
}
//Create i.<prop> == <value> dynamically
static Expression<Func<TType, bool>> BuildPredicate<TType>(string property, object value)
{
var itemParameter = Expression.Parameter(typeof(TType), "i");
var expression = Expression.Lambda<Func<TType, bool>>(
Expression.Equal(
Expression.MakeMemberAccess(
itemParameter,
typeof(TType).GetProperty(property)),
Expression.Constant(value)
),
itemParameter);
return expression;
}
}
I don't really get why would you need the Dynamic LINQ here? Are the item properties not known at compile-time? If you can access a given item properties by name, eg. var prop = myitem['Color'], you don't need Dynamic LINQ.
It depends on how you render the results. There is a lot of ways to achieve the desired behavior, in general:
Fully client-side. If you do everything client-side (fetching data, rendering, paging) - jQuery would be the best way to go.
Server-side + client-side. If you render results on the server, you may add HTML attributes (for each property) to each search result markup and filter those client-side. The only problem in this case can be paging (if you do paging server-side, you will be able to filter the current page only)
Fully server-side. Post the form with search parameters and narrow down the search results using LINQ - match the existing items' properties with form values.
EDIT
If I were you (and would need to filter results server-side), I'd do something like:
var filtered = myItems.Where(i => i.Properties.Match(formValues))
where Match is an extension method that checks if a given list of properties matches provided values. Simple as this - no Dynamic LINQ needed.
EDIT 2
Do you need to map the LINQ query to the database query (LINQ to SQL)? That would complicate things a bit, but is still doable by chaining multiple .Where(...) clauses. Just loop over the filter properties and add .Where(...) to the query from previous iteration.
you may have a look at PredicateBuilder from the author of C# 4.0 in a Nutshell
As already pointed out by #Piotr Szmyd probabbly you don't need dynamic Linq. Iterating over all properties of T doesn'require dynamic linq. Dynamic Linq is mainly usefull to build complete queries on the client side and send it in string format to the server.
However now, it become obsolete, since Mvc 4 supports client side queries through Api Controllers returning an IQueryable.
If you just need to iterate over all properties of T you can do it with reflection and by building the LambdaExpressions that will compose the filtering criterion. You can do it with the static methods of the Expression class.
By using such static methods you can build dynamically expressions like m => m.Name= "Nick" with a couple instructions...than you put in and them...done you get and expression you can apply to an exixting IQueryable
LINQ implementation still has not changed so there should be no problem using the dynamic LINQ library. It simply creates LINQ expressions from strings.
You can use AJAX to call action methods that run the LINQ query and return JSON data. JQuery would populate HTML from the returned data.
I have the following code -
public void LoadAllContacts()
{
var db = new ContextDB();
var contacts = db.LocalContacts.ToList();
grdItems.DataSource = contacts.OrderBy(x => x.Areas.OrderBy(y => y.Name));
grdItems.DataBind();
}
I'm trying to sort the list of the contacts according to the area name that is contained within each contact. When I tried the above, I get "At least one object must implement IComparable.". Is there an easy way instead of writing a custom IComparer?
Thanks!
try this:
public void LoadAllContacts()
{
var db = new ContextDB();
var contacts = db.LocalContacts.ToList();
grdItems.DataSource = contacts.OrderBy(x => x.Areas.OrderBy(y => y.Name).First().Name);
grdItems.DataBind();
}
this will order the contacts by the first area name, after ordering the areas by name.
Hope this helps :)
Edit: fixed error in code. (.First().Name)
I was in a discussion with #AbdouMoumen but in the end I thought I'd provide my own answer :-)
His answer works, but there two performance issues in this code (both in the answer as in the original question).
First, the code loads ALL contacts in the db. This may or may not be a problem, but in general I would recommend NOT to do this. Many modern controls support paging/filtering out of the box, so you'd be better off supplying an not-yet-evaluated IQueryable<T> instead of List<T>. If however you need everything in memory, you should delay the ToList to the last possible moment.
Second, in AbdouMoumen's answer, there is a so-called 'SELECT N+1' problem. Entity Framework will by default use lazy loading to fetch additional properties. I.e. the Areas property will not be fetched from the database until it's accessed. In this case this will happen in the controls 'for loop', while it's ordering the result set by name.
Open up SQL Server Profiler to see what I mean: you will see a SELECT statement for all the contacts, and an additional SELECT statement for each contact that fetches the Areas for that contact.
A much better solution would be the following:
public void LoadAllContacts()
{
using (var db = new ContextDB())
{
// note: no ToList() yet, just defining the query
var contactsQuery = db.LocalContacts
.OrderBy(x => x.Areas
.OrderBy(y => y.Name)
.First().Name);
// fetch all the contacts, correctly ordered in the DB
grdItems.DataSource = contactsQuery.ToList();
grdItems.DataBind();
}
}
Is it one to one relation (Contact->Area)?
if yeah then try the following :
public partial class Contact
{
public string AreaName
{
get
{
if (this.Area != null)
return this.Area.Name;
return string.Empty;
}
}
}
then
grdItems.DataSource = contacts.OrderBy(x => x.AreaName);
I am looking to get a list of the column names returned from a Model. Anyone know how this would be done, any help would be greatly appreciated.
Example Code:
var project = db.Projects.Single(p => p.ProjectID.Equals(Id));
This code would return the Projects object, how would I get a list of all the column names in this Model.
Thanks
This would be nice to have as an extension method:
public static class LinqExtensions
{
public static ReadOnlyCollection<MetaDataMember> ColumnNames<TEntity> (this DataContext source)
{
return source.Mapping.MappingSource.GetModel (typeof (DataContext)).GetMetaType (typeof (TEntity)).DataMembers;
}
}
example:
var columnNames = myDataContext.ColumnNames<Orders> ();
Thanks guys, you got me started on the right track. I found my solution with the following code. I can then iterate through the DataMembers and pull out their individual properties such as name, type, etc.
var db = new GMPDataContext();
var columnNames = db.Mapping.MappingSource
.GetModel(typeof(GMPDataContext))
.GetMetaType(typeof(Project))
.DataMembers;
Your Projects wrapper will have a set of properties each with a [Column] attribute. So just use reflection to enumerate the properties with that attribute.
Using Todd Smiths(+1) solution you get all properties (included entity sets, etc).
To filter out all non-column properties this will do the trick:
var columnNames = db.ColumnNames<Orders>().Where(n => n.Member.GetCustomAttributes(typeof(System.Data.Linq.Mapping.ColumnAttribute), false).FirstOrDefault() != null).Select(n => n.Name);
I am sorry, I don't have working experience with LINQ.
This is purely based on looking at MSDN.
DataContext has a Mapping property, which returns an instance of MetaModel.
MetaModel has GetMetaType, which takes a Type. In your case it could be typeof(Project).
GetMetaType returns a MetaType which has the GetDataMember method, which takes a MemberInfo parameter. You will have to use reflection on your Projects object to get the MemberInfo object.
The MetaDataMember instance returned by GetDataMember should have all the things, you need.
I hope I am somewhat in right direction (purely looking at MSDN & traversing)
Your columns should be mapped as properties on your Project model. I'm not sure if you can get the underlying database structure when using LINQ to SQL. The entire point of LINQ to SQL is to abstract the database away.
Here an another way:
public string[] GetColumnNames()
{
var propnames = GetPropertyNames(_context.Users);
return propnames.ToArray();
}
static IEnumerable<string> GetPropertyNames<T>(IEnumerable<T> lst)
{
foreach (var pi in typeof(T).GetProperties())
{
yield return pi.Name;
}
}