I have a LinqToXML expression where I am trying to select distinct names based on similar attributes. The code is working great and I've put it below:
var q = xmlDoc.Element("AscentCaptureSetup").Element("FieldTypes")
.Descendants("FieldType")
.Select(c => new { width = c.Attribute("Width").Value,
script = c.Attribute("ScriptName").Value,
sqlType = c.Attribute("SqlType").Value,
enableValues = c.Attribute("EnableValues").Value,
scale = c.Attribute("Scale").Value,
forceMatch = c.Attribute("ForceMatch").Value,
forceMatchCaseSensitive = c.Attribute("ForceMatchCaseSensitive").Value,
sortAlphabetically = c.Attribute("SortAlphabetically").Value,
})
.Distinct();
The problem arises since not all the attributes are required, and if one of them is omitted, for example sortAlphabetically, I get an Object not Referenced error. Makes sense, but it there a way to alter the query to only use assign the new values if the attribute actually exists? (Thereby bypassing any null pointer errors)
Instead of using the Value property (which will blow up on a null reference), simply cast the XAttribute to string - you'll either get the value, or a null reference if the XAttribute reference is null. (XElement works the same way, and this applies to all conversions to nullable types.)
So you'd have:
.Select(c => new {
width = (string) c.Attribute("Width"),
script = (string) c.Attribute("ScriptName"),
sqlType = (string) c.Attribute("SqlType"),
enableValues = (string) c.Attribute("EnableValues"),
scale = (string) c.Attribute("Scale"),
forceMatch = (string) c.Attribute("ForceMatch"),
forceMatchCaseSensitive = (string) c.Attribute("ForceMatchCaseSensitive"),
sortAlphabetically = (string) c.Attribute("SortAlphabetically"),
})
Some of those attributes sound like they should actually be cast to int? or bool?, mind you...
Related
I am trying to update values in table emp. Which column to update is dynamic.
public void updateEmployees(List<String> columnDb, List<String> columnValues)
{
var data = ctx.tblEmployee.Where(e => e.Id == empId).Select(e => e).SingleOrDefault();
....
data.columnDb = columnValues; // Pseudo
ctx.tblEmployee.Add(data);
ctx.SaveChanges();
}
How to update columns which are passed dynamically as a parameter?
You can do this with the power of Reflection.
Just iterate through properties of your object and set the value for the properties that you have in your list.
First, let's build a dictionary with property names and values from your parameters to make the value access easier:
var values = columnDb.Zip(columnValues,
(name, value) => new { Name = name, Value = value })
.ToDictionary(x => x.Name, x => x.Value);
Now, iterate through properties and set values:
var data = ctx.tblEmployee.SingleOrDefault(e => e.Id == empId);
foreach(PropertyInfo property in data.GetType().GetProperties())
{
// Check if property should be updated
if(values.ContainsKey(property.Name))
{
var value = values[property.Name];
// Change the type of the value to the type of the property
object converted = Convert.ChangeType(value, property.PropertyType);
// Set the property value
property.SetValue(data,values[property.Name]);
}
}
Of course, the code above assumes that there is a conversion between string and the type of the properties of your data object.
In sql server I create views where I can check for null values and replace them with a default if I want (i.e. ISNULL(PrimaryPhone, 'No Primary #') AS PrimaryPhone. I used a lot of views in my asp.net web forms application, but I am now learning MVC 4 and want to start out right.
I have a model, controller and view set up for my client table. I would like to be able to replace null/empty values with ("Not Entered") or something like that.
I believe this needs to go in the controller, please correct me if I'm wrong.
I saw an example that uses hasvalue, but it is not available through intellisense.
How would I replace empty/null values without using DefaultValue in my model?
Thanks
var result = db.Clients.Select(x => new
{
CustomerID = x.CustomerID,
UserID = x.UserID,
FullName = x.FullName,
EmailAdd = x.emailadd.DefaultIfEmpty("No Email"),....
You can use the ?? operator to set a default value when something is null:
var result = db.Clients.Select(x => new
{
CustomerID = x.CustomerID,
UserID = x.UserID,
FullName = x.FullName,
EmailAdd = x.emailadd ?? "No Email", ...
If you need more control, for example checking for both null and empty, you can also use the ?: operator (also known as the "conditional operator" or "ternary operator"):
var result = db.Clients.Select(x => new
{
CustomerID = x.CustomerID,
UserID = x.UserID,
FullName = x.FullName,
EmailAdd = string.IsNullOrEmpty(x.emailadd) ? "No Email" : x.emailadd, ...
Following Linq to Entities query is causing the "Unable to create a constant value of type 'Data.InhouseUnit'. Only primitive types ('such as Int32, String, and Guid') are supported in this context" exception.
IList<FaultReport> faultReports = (from fr in _session.FaultReports
where fr.CreatedOn > dateTime
select new FaultReport
{
Id = fr.Id,
ExecutionDate = fr.ExecutionDate ?? DateTime.MinValue,
FaultType = fr.FaultType,
Quarters = fr.Quarters,
InhouseSpaceId = fr.InhouseSpaceId,
InhouseSpace = new InhouseSpace { Id = fr.InhouseSpace.Id, Name = fr.InhouseSpace.Name },
InhouseUnitId = fr.InhouseUnitId ?? Guid.Empty,
**InhouseUnit = fr.InhouseUnitId == Guid.Empty ? null : new InhouseUnit { Id = fr.InhouseUnit.Id, Name = fr.InhouseUnit.Name }**
}).ToList();
Specifically, it is the if expression in bold font which causes the exception. I need to make the check as fr.InhouseUnitId is a nullable. If I take out the the bolded expression, the rest of the statement works just fine. I have spent a fair amount of time, in msdn forum and on web, to understand what is causing the exception but still cannot quite understand. Guid is scalar so it should work, right? Even this expression InhouseUnit = true ? null: new InhouseUnit() in place of the bolded expression in the above statement wouldn't work. Can we even write if/else
If i try to write an extension method to take away the logic and just return a result, following exception is thrown:
LINQ to Entities does not recognize the method 'System.Object
GuidConversion(System.Nullable`1[System.Guid], System.Object)' method, and this method
cannot be translated into a store expression
It looks like you are projecting into new objects of the same type that you are querying from. Is that the case? It seems a little weird, but assuming you have a good reason for doing this, you could split the query into two parts. The first part would get what you need from the database. The second part would run locally (i.e. LINQ-to-Objects) to give you the projection you need. Something like this:
var query =
from fr in _session.FaultReports
where fr.CreatedOn > dateTime
select new {
fr.Id,
fr.ExecutionDate,
fr.FaultType,
fr.Quarters,
InhouseSpaceId = fr.InhouseSpace.Id,
InhouseSpaceName = fr.InhouseSpace.Name,
InhouseUnitId = fr.InhouseUnit.Id,
InhouseUnitName = fr.InhouseUnit.Name,
};
IList<FaultReport> faultReports = (
from fr in query.ToList()
select new FaultReport {
Id = fr.Id,
ExecutionDate = fr.ExecutionDate ?? DateTime.MinValue,
FaultType = fr.FaultType,
Quarters = fr.Quarters,
InhouseSpaceId = fr.InhouseSpaceId,
InhouseSpace = new InhouseSpace { Id = fr.InhouseSpaceId, Name = fr.InhouseSpaceName },
InhouseUnitId = fr.InhouseUnitId ?? Guid.Empty,
InhouseUnit = fr.InhouseUnitId == Guid.Empty ? null : new InhouseUnit { Id = fr.InhouseUnitId, Name = fr.InhouseUnitName }
}).ToList();
I am having some trouble with a linq query I am trying to write.
I am trying to use the repository pattern without to much luck. Basically I have a list of transactions and a 2nd list which contains the description field that maps against a field in my case StoreItemID
public static IList<TransactionViewModel> All()
{
var result = (IList<TransactionViewModel>)HttpContext.Current.Session["Transactions"];
if (result == null)
{
var rewardTypes = BusinessItemRepository.GetItemTypes(StoreID);
HttpContext.Current.Session["Transactions"] =
result =
(from item in new MyEntities().TransactionEntries
select new TransactionViewModel()
{
ItemDescription = itemTypes.FirstOrDefault(r=>r.StoreItemID==item.StoreItemID).ItemDescription,
TransactionDate = item.PurchaseDate.Value,
TransactionAmount = item.TransactionAmount.Value,
}).ToList();
}
return result;
}
public static List<BusinessItemViewModel>GetItemTypes(int storeID)
{
var result = (List<BusinessItemViewModel>)HttpContext.Current.Session["ItemTypes"];
if (result == null)
{
HttpContext.Current.Session["ItemTypes"] = result =
(from items in new MyEntities().StoreItems
where items.IsDeleted == false && items.StoreID == storeID
select new BusinessItemViewModel()
{
ItemDescription = items.Description,
StoreID = items.StoreID,
StoreItemID = items.StoreItemID
}).ToList();
}
return result;
However I get this error
Unable to create a constant value of type 'MyMVC.ViewModels.BusinessItemViewModel'. Only primitive types ('such as Int32, String, and Guid') are supported in this context.
I know its this line of code as if I comment it out it works ok
ItemDescription = itemTypes.FirstOrDefault(r=>r.StoreItemID==item.StoreItemID).ItemDescription,
How can I map ItemDescription against my list of itemTypes?
Any help would be great :)
This line has a problem:
ItemDescription = itemTypes.FirstOrDefault(r=>r.StoreItemID==item.StoreItemID)
.ItemDescription,
Since you are using FirstOrDefault you will get null as default value for a reference type if there is no item that satifies the condition, then you'd get an exception when trying to access ItemDescription - either use First() if there always will be at least one match or check and define a default property value for ItemDescription to use if there is none:
ItemDescription = itemTypes.Any(r=>r.StoreItemID==item.StoreItemID)
? itemTypes.First(r=>r.StoreItemID==item.StoreItemID)
.ItemDescription
: "My Default",
If itemTypes is IEnumerable then it can't be used in your query (which is what the error message is telling you), because the query provider doesn't know what to do with it. So assuming the that itemTypes is based on a table in the same db as TransactionEntities, then you can use a join to achieve the same goal:
using (var entities = new MyEntities())
{
HttpContext.Current.Session["Transactions"] = result =
(from item in new entities.TransactionEntries
join itemType in entities.ItemTypes on item.StoreItemID equals itemType.StoreItemID
select new TransactionViewModel()
{
ItemDescription = itemType.ItemDescription,
TransactionDate = item.PurchaseDate.Value,
TransactionAmount = item.TransactionAmount.Value,
CustomerName = rewards.CardID//TODO: Get customer name
}).ToList();
}
I don't know the structure of your database, but hopefully you get the idea.
I had this error due a nullable integer in my LINQ query.
Adding a check within my query it solved my problem.
query with problem:
var x = entities.MyObjects.FirstOrDefault(s => s.Obj_Id.Equals(y.OBJ_ID));
query with problem solved:
var x = entities.MyObjects.FirstOrDefault(s => s.Obj_Id.HasValue && s.Obj_Id.Value.Equals(y.OBJ_ID));
If I create this collection:
IEnumerable<_TITLE> _titles = null;
How can I set the result set from Netflix in this expression:
_titles = from t in Titles where t.Id == "ApUFq" select new {t, t.Cast}
I am getting:
Cannot implicitly convert type
'System.Linq.IQueryable'
to
'System.Collections.Generic.IEnumerable<_Title>'.
An explicit conversion exists (are you
missing a cast?)
I understand it's because I am using an anonymous type. _TITLE is a custom complex object I create that exposes a subset of Netflix properties.
If I add "_TITLE" in front the of the "new" it says that my object does not implement IENUMBERABLE.
If then _TITLE implements IENUMBERABLE, it says _TITLE does not contain a definition for ADD and still getting conversion error.
Basically, I want to set the _TITLE properties with the data returned from Netflix. I have defined _TITLE to contain the fields I need, plus a collection of PERSON (for Cast).
If your generic type is _TITLE, then you need to do select new _TITLE {Prop = Value}.
If you intend to use a generic type, then you need to use var:
var _titles = from t in Titles where t.Id == "ApUFq" select new {t, t.Cast};
So perhaps this is what you meant:
var _titles = from t in Titles where t.Id == "ApUFq" select new _TITLE {Title = t};
Something along those lines. var can be used even if you don't intend to use an anonymous type.
In addition to vcsjones's answer, You don't need to implement IEnumerable on _TITLE. What's going on is that when you write
var foo = new TYPENAME { a, b };
it means:
create a new TYPENAME, which implements IEnumerable
call foo.Add(a) then foo.Add(b);
Example:
var names = new List<string> { "Joe", "Mary", "Susan" };
As vcsjones mentioned, You need to use Parameter names when initializing an object, or perhaps you meant to use parentheses and call a constructor
var title = new _TITLE { Title = t.ID, Cast = t.Cast };
// or
var title = new _TITLE (t.ID, t.Cast);