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;
}
}
Related
I am using the repository pattern with Entity Framework as described in this article: repository pattern with Entity Framework
In the part where the GenericRepository is described (Generic Repository) there is a method which is used to get entities from the database set called Get. It has an orderBy but no groupBy. I am wondering how one might implement a groupBy in the same manner as the orderBy so that you can specify which field to group by dynamically on the entity.
What I have come up with is this:
Func<IQueryable<TEntity>, IGrouping<string, TEntity>> groupBy = null
and then in the method code it should be used something like this:
if(groupBy != null)
{
query = groupBy(query).ToList();
}
But this is not compiling since the IGrouping is not queryable. Does someone know how to point me in the right direction or has a solution to this?
Edit: The reason for doing this instead of using groupby on the returned list is for performance reasons. I want the groupby to be sent as an sql statement to the database and resolved there.
Grouping has no sense without projection. So you have to define new method which returns IEnumerable with new type.
I have added sample of such method. Also removed includeProperties because EF Core ignores Includes during grouping.
Usage sample:
_orderRepostory
.GetGrouped(e => e.UserId, g => new { UserId = g.Key, Count = g.Count()});
And implementation:
public class GenericRepository<TEntity> where TEntity : class
{
... // other code
public virtual IEnumerable<TResult> GetGrouped<TKey, TResult>(
Expression<Func<TEntity, TKey>> groupingKey,
Expression<Func<IGrouping<TKey, TEntity>, TResult>> resultSelector,
Expression<Func<TEntity, bool>>? filter = null)
{
var query = dbSet.AsQueryable();
if (filter != null)
{
query = query.Where(filter);
}
return query.GroupBy(groupingKey).Select(resultSelector);
}
}
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);
It seems as if only DataSet, DataTable and DataView can be used as sources when you want to use BindingSource.Find. I'm binding IQueryable and IEnumerable to my binding source, but would very much like to enjoy the 'convenience' of the BindingSource.Find method, without writing reams of code myself, as time is of the essence.
Does anyone know of an existing implementation, or at least detailed 'how to' article that can help me achieve this?
You can use the Type.GetProperty and Array.FindIndex methods to create a concise extension method.
public static int Find<T>(this IEnumerable<T> items, string propertyName, Object key)
{
PropertyInfo property = typeof(T).GetProperty(propertyName);
if(property == null)
{
throw new ArgumentException(String.Format("Type {0} contains no property named \"{1}\". ",
typeof(T).Name, propertyName), "propertyName");
}
return Array.FindIndex(items.ToArray(), i => Object.Equals(property.GetValue(i, null), key));
}
I know there is a way to use Expressions and Lambdas to accomplish this but I having a hard time piecing it all together. All I need is a method that will dynamically query an Entity Framework DBSet object to find the row where the propery with the given name matches the value.
My context:
public class MyContext : DbContext
{
public IDbSet<Account> Accoounts{ get { return Set<Account>(); } }
}
The method that I'm looking to write:
public T Get<T>(string property, object value) : where T is Account
{...}
I would rather not have to use Dynamic SQL to accomplish this so no need to suggest it because I already know it's possible. What I'm really looking for is some help to accomplish this using Expressions and Lambdas
Thanks in advance, I know it's brief but it should be pretty self-explanatory. Comment if more info is needed
I'm trying to avoid dynamic linq as much as possible because the main point of linq is strongly typed access. Using dynamic linq is a solution but it is exactly the oppose of the linq purpose and it is quite close to using ESQL and building the query from sting concatenation. Anyway dynamic linq is sometimes real time saver (especially when it comes to complex dynamic ordering) and I successfully use it in a large project with Linq-to-Sql.
What I usually do is defining some SearchCriteria class like:
public class SearchCriteria
{
public string Property1 { get; set; }
public int? Property2 { get; set; }
}
And helper query extension method like:
public static IQueryable<SomeClass> Filter(this IQueryable<SomeClass> query, SearchCriteria filter)
{
if (filter.Property1 != null) query = query.Where(s => s.Property1 == filter.Property1);
if (filter.Property2 != null) query = query.Where(s => s.Property2 == filter.Property2);
return query;
}
It is not generic solution. Again generic solution is for some strongly typed processing of classes sharing some behavior.
The more complex solution would be using predicate builder and build expression tree yourselves but again building expression tree is only more complex way to build ESQL query by concatenating strings.
Here's my implementation:
public T Get<T>(string property, object value) : where T is Account
{
//p
var p = Expression.Parameter(typeof(T));
//p.Property
var propertyExpression = Expression.Property(p, property);
//p.Property == value
var equalsExpression = Expression.Equal(propertyExpression, Expression.Constant(value));
//p => p.Property == value
var lambda = Expression.Lambda<Func<T,bool>>(equalsExpression, p);
return context.Set<T>().SingleOrDefault(lambda);
}
It uses EF 5's Set<T>() method. If you are using a lower version, you'll need to implement a way of getting the DbSet based on the <T> type.
Hope it helps.
Dynamic Linq may be an option. Specify your criteria as a string and it will get built as an expression and ran against your data;
An example from something I have done;
var context = new DataContext(ConfigurationManager.ConnectionStrings["c"].ConnectionString);
var statusConditions = "Status = 1";
var results = (IQueryable)context.Contacts.Where(statusConditions);
http://weblogs.asp.net/scottgu/archive/2008/01/07/dynamic-linq-part-1-using-the-linq-dynamic-query-library.aspx
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);