Hi I want to set the value in the list of objects that matches the given condition in the where clause.Is it possible?
Other work around is to get the list of objects using where clause and then iterate using for Or foreach loop and update the value.
listOfRequestAssigned.Where(x => x.RequestedNumber == CurrentRequest);
I have list listOfRequestAssigned of objects and want to update some propery of the objects that match my search criteria.
class Request
{
bool _requestCompleted;
int _requestedNumber;
public int RequestedNumber
{
get { return _requestedNumber; }
set { _requestedNumber = value; }
}
public bool RequestCompleted
{
get { return _requestCompleted; }
set { _requestCompleted = value; }
}
}
I want to update RequestCompleted property of all objects that match criteria using Linq
You can use ForEach in Linq
listOfRequestAssigned.Where(x => x.RequestedNumber == CurrentRequest).ToList().ForEach(x => x.RequestCompleted = true);
if you have more than one update to do,
listOfRequestAssigned.Where(x => x.RequestedNumber == CurrentRequest).ToList().ForEach(x => { x.RequestCompleted = true; x.OtherProperty = value; } );
Where(...) give you a query, not a Request or a List<Request>. Use FirstOrDefault() if you want to have one (or 0) result, or ToList() if you want to have a list of results on wich you can use ForEach().
In general Linq is a query- not an update tool, but you can use a foreach:
var currentRequests = listOfRequestAssigned
.Where(x => x.RequestedNumber == CurrentRequest);
foreach(var req in currentRequests)
{
req.RequestCompleted = true;
}
Since you have specific collection of type List, you can just use ForEach and a conditional set:
listOfRequestAssigned.Foreach(x => { if (x.RequestedNumber == CurrentRequest) x.RequestCompleted = true;}});
If you had a more generic collection IEnumerable, you can use Select in Linq to build a projection where property will be set as desired (original collection will be left untouched!):
listOfRequestAssigned
.Where(x => x.RequestedNumber == CurrentRequest)
.Select(x => { x.RequestCompleted = true; return x; })
You can use to assign boolean value by following on comparing time. This is the very simplest and smart way for bool property.
listOfRequestAssigned.ForEach(x => x.RequestCompleted = x.RequestedNumber
== CurrentRequest);
Related
in LINQ how do i search all fields in a table, what do i put for ANYFIELD in the below?
Thanks
var tblequipments = from d in db.tblEquipments.Include(t => t.User).Include(t => t.ChangeLog).Include(t => t.AssetType)
where d."ANYFIELD" == "VALUE" select d;
You can't. You must compare each field individually. It doesn't make sense to compare all fields, given a field may not even be of the same type as the object you're comparing to.
You can, using reflection. Try this:
static bool CheckAllFields<TInput, TValue>(TInput input, TValue value, bool alsoCheckProperties)
{
Type t = typeof(TInput);
foreach (FieldInfo info in t.GetFields().Where(x => x.FieldType == typeof(TValue)))
{
if (!info.GetValue(input).Equals(value))
{
return false;
}
}
if (alsoCheckProperties)
{
foreach (PropertyInfo info in t.GetProperties().Where(x => x.PropertyType == typeof(TValue)))
{
if (!info.GetValue(input, null).Equals(value))
{
return false;
}
}
}
return true;
}
And your LINQ query:
var tblequipments = from d in db.tblEquipments.Include(t => t.User).Include(t => t.ChangeLog).Include(t => t.AssetType)
where CheckAllFields(d, "VALUE", true) select d;
The third parameter should be true if you want to check all fields and all properties, and false if you want to check only all fields.
EDIT: Someone already built this...see here.
Not a full answer, but I don't agree with assertion that you simply can't...
You could come up with an extension method that dynamically filtered the IQueryable/IEnumerable (I'm guessing IQueryable by the db variable) based on properties of a similar type for you. Here's something whipped up in Linqpad. It references PredicateBuilder and is by no means complete/fully accurate, but I tested it out in Linq-to-SQL on some of my tables and it worked as described.
void Main()
{
YourDbSet.WhereAllPropertiesOfSimilarTypeAreEqual("A String")
.Count()
.Dump();
}
public static class EntityHelperMethods
{
public static IQueryable<TEntity> WhereAllPropertiesOfSimilarTypeAreEqual<TEntity, TProperty>(this IQueryable<TEntity> query, TProperty value)
{
var param = Expression.Parameter(typeof(TEntity));
var predicate = PredicateBuilder.True<TEntity>();
foreach (var fieldName in GetEntityFieldsToCompareTo<TEntity, TProperty>())
{
var predicateToAdd = Expression.Lambda<Func<TEntity, bool>>(
Expression.Equal(
Expression.PropertyOrField(param, fieldName),
Expression.Constant(value)), param);
predicate = predicate.And(predicateToAdd);
}
return query.Where(predicate);
}
// TODO: You'll need to find out what fields are actually ones you would want to compare on.
// This might involve stripping out properties marked with [NotMapped] attributes, for
// for example.
private static IEnumerable<string> GetEntityFieldsToCompareTo<TEntity, TProperty>()
{
Type entityType = typeof(TEntity);
Type propertyType = typeof(TProperty);
var fields = entityType.GetFields()
.Where (f => f.FieldType == propertyType)
.Select (f => f.Name);
var properties = entityType.GetProperties()
.Where (p => p.PropertyType == propertyType)
.Select (p => p.Name);
return fields.Concat(properties);
}
}
Useful resources for the unresolved part:
Finding the relevant properties
if this help some one.
first find all properties within Customer class with same type as query:
var stringProperties = typeof(Customer).GetProperties().Where(prop =>
prop.PropertyType == query.GetType());
then find all customers from context that has at least one property with value equal to query:
context.Customer.Where(customer =>
stringProperties.Any(prop =>
prop.GetValue(customer, null) == query));
I was trying to implement the jQgrid using MvcjQgrid and i got this exception.
System.NotSupportedException was unhandled by user code
Message=The method 'Skip' is only supported for sorted input in LINQ to Entities. The method 'OrderBy' must be called before the method 'Skip'.
Though OrdeyBy is used before Skip method why it is generating the exception? How can it be solved?
I encountered the exception in the controller:
public ActionResult GridDataBasic(GridSettings gridSettings)
{
var jobdescription = sm.GetJobDescription(gridSettings);
var totalJobDescription = sm.CountJobDescription(gridSettings);
var jsonData = new
{
total = totalJobDescription / gridSettings.PageSize + 1,
page = gridSettings.PageIndex,
records = totalJobDescription,
rows = (
from j in jobdescription
select new
{
id = j.JobDescriptionID,
cell = new[]
{
j.JobDescriptionID.ToString(),
j.JobTitle,
j.JobType.JobTypeName,
j.JobPriority.JobPriorityName,
j.JobType.Rate.ToString(),
j.CreationDate.ToShortDateString(),
j.JobDeadline.ToShortDateString(),
}
}).ToArray()
};
return Json(jsonData, JsonRequestBehavior.AllowGet);
}
GetJobDescription Method and CountJobDescription Method
public int CountJobDescription(GridSettings gridSettings)
{
var jobdescription = _dataContext.JobDescriptions.AsQueryable();
if (gridSettings.IsSearch)
{
jobdescription = gridSettings.Where.rules.Aggregate(jobdescription, FilterJobDescription);
}
return jobdescription.Count();
}
public IQueryable<JobDescription> GetJobDescription(GridSettings gridSettings)
{
var jobdescription = orderJobDescription(_dataContext.JobDescriptions.AsQueryable(), gridSettings.SortColumn, gridSettings.SortOrder);
if (gridSettings.IsSearch)
{
jobdescription = gridSettings.Where.rules.Aggregate(jobdescription, FilterJobDescription);
}
return jobdescription.Skip((gridSettings.PageIndex - 1) * gridSettings.PageSize).Take(gridSettings.PageSize);
}
And Finally FilterJobDescription and OrderJobDescription
private static IQueryable<JobDescription> FilterJobDescription(IQueryable<JobDescription> jobdescriptions, Rule rule)
{
if (rule.field == "JobDescriptionID")
{
int result;
if (!int.TryParse(rule.data, out result))
return jobdescriptions;
return jobdescriptions.Where(j => j.JobDescriptionID == Convert.ToInt32(rule.data));
}
// Similar Statements
return jobdescriptions;
}
private IQueryable<JobDescription> orderJobDescription(IQueryable<JobDescription> jobdescriptions, string sortColumn, string sortOrder)
{
if (sortColumn == "JobDescriptionID")
return (sortOrder == "desc") ? jobdescriptions.OrderByDescending(j => j.JobDescriptionID) : jobdescriptions.OrderBy(j => j.JobDescriptionID);
return jobdescriptions;
}
The exception means that you always need a sorted input if you apply Skip, also in the case that the user doesn't click on a column to sort by. I could imagine that no sort column is specified when you open the grid view for the first time before the user can even click on a column header. To catch this case I would suggest to define some default sorting that you want when no other sorting criterion is given, for example:
switch (sortColumn)
{
case "JobDescriptionID":
return (sortOrder == "desc")
? jobdescriptions.OrderByDescending(j => j.JobDescriptionID)
: jobdescriptions.OrderBy(j => j.JobDescriptionID);
case "JobDescriptionTitle":
return (sortOrder == "desc")
? jobdescriptions.OrderByDescending(j => j.JobDescriptionTitle)
: jobdescriptions.OrderBy(j => j.JobDescriptionTitle);
// etc.
default:
return jobdescriptions.OrderBy(j => j.JobDescriptionID);
}
Edit
About your follow-up problems according to your comment: You cannot use ToString() in a LINQ to Entities query. And the next problem would be that you cannot create a string array in a query. I would suggest to load the data from the DB with their native types and then convert afterwards to strings (and to the string array) in memory:
rows = (from j in jobdescription
select new
{
JobDescriptionID = j.JobDescriptionID,
JobTitle = j.JobTitle,
JobTypeName = j.JobType.JobTypeName,
JobPriorityName = j.JobPriority.JobPriorityName,
Rate = j.JobType.Rate,
CreationDate = j.CreationDate,
JobDeadline = j.JobDeadline
})
.AsEnumerable() // DB query runs here, the rest is in memory
.Select(a => new
{
id = a.JobDescriptionID,
cell = new[]
{
a.JobDescriptionID.ToString(),
a.JobTitle,
a.JobTypeName,
a.JobPriorityName,
a.Rate.ToString(),
a.CreationDate.ToShortDateString(),
a.JobDeadline.ToShortDateString()
}
})
.ToArray()
I had the same type of problem after sorting using some code from Adam Anderson that accepted a generic sort string in OrderBy.
After getting this excpetion, i did lots of research and found that very clever fix:
var query = SelectOrders(companyNo, sortExpression);
return Queryable.Skip(query, iStartRow).Take(iPageSize).ToList();
Hope that helps !
SP
I have a list of prices ordered by date. I need to select all monotonously decreasing values. The following code works:
public static List<DataPoint> SelectDecreasingValues(List<DataPoint> dataPoints)
{
var ret = new List<DataPoint>(dataPoints.Count);
var previousPrice = dataPoints[0].Price;
for (int i = 0; i < dataPoints.Count; i++)
{
if (dataPoints[i].Price <= previousPrice)
{
ret.Add(dataPoints[i]);
previousPrice = dataPoints[i].Price;
}
}
return ret;
}
However, is there a shorter/cleaner way to accomplish it with Linq?
This code is equivalent:
previousPrice = dataPoints[0].Price;
var ret = dataPoints.Where(x => {
if(x.Price <= previousPrice)
{ previousPrice = x.Price; return true;}
return false;
}).ToList();
However, if you don't need to have a list, go with plain enumerables and drop the ToList at the end. That way you can make use of the deferred execution feature built into LINQ.
The following code is also equivalent:
DataPoint previous = dataPoints.FirstOrDefault();
var ret = dataPoints.Where(x => x.Price <= previous.Price)
.Select(x => previous = x).ToList();
This works because of the deferred execution in LINQ. For each item in dataPoints it will first execute the Where part and then the Select part and only then will it move to the second item in dataPoints.
You need to decide which version you want to use. The second one is not as intention revealing as the first one, because you need to know about the internal workings of LINQ.
public IEnumerable<T> WhereMonotonicDecreasing<T>(
IEnumerable<T> source,
Func<T, IComparable> keySelector)
{
IComparable key;
bool first = true;
foreach(T t in source)
{
if (first)
{
key = keySelector(t);
yield return t;
first = false;
}
else
{
IComparable newKey = keySelector(t);
if (newKey.CompareTo(key) < 0)
{
key = newKey;
yield return t;
}
}
}
}
Called by:
dataPoints.WhereMonotonicDecreasing(x => x.Price);
previousPrice = dataPoints[0];
dataPoints.Where(p => p.Price <= previousPrice.Price)
.Select(p => previousPrice = p);
You can then use .ToList() if you really need one.
How about (untested):
return dataPoints.Take(1)
.Concat(dataPoints.Skip(1)
.Zip(dataPoints,
(next, previous) =>
new { Next = next, Previous = previous })
.Where(a => a.Next.Price <= a.Previous.Price)
.Select(a => a.Next))
.ToList();
Essentially, this overlays a "one-deferred" version of the sequence over the sequence to produce "next, previous" tuples and then applies the relevant filters on those tuples. The Take(1) is to pick the first item of the sequence, which it appears you always want.
If you don't care for the readability of the variable names, you could shorten it to:
return dataPoints.Take(1)
.Concat(dataPoints.Skip(1)
.Zip(dataPoints, Tuple.Create)
.Where(a => a.Item1.Price <= a.Item2.Price)
.Select(a => a.Item1))
.ToList();
I have a settingspropertyvaluecollection.I dont want to loop through all the properties using a for each loop.Instead i want to query the collection.How do i do that?is there a way to use LINQ and do it?
Thanks
SettingsPropertyValueCollection doesn't implement IEnumerable<T> but it does implement IEnumerable. If you want to query it using LINQ you have a couple of options.
You could create a Where() extension method that takes IEnumerable and a query and performs the query for you:
public static class IEnumerableExtensions
{
public static IEnumerable<T> Where<T>(this IEnumerable input, Func<T,bool> query)
{
return input.Cast<T>().Where(item => query(item));
}
}
assuming:
var settings = new SettingsPropertyValueCollection
{
new SettingsPropertyValue(new SettingsProperty("Email")
{
DefaultValue = "a#a.com",
PropertyType = typeof(string)
}),
new SettingsPropertyValue(new SettingsProperty("City")
{
DefaultValue = "Austin",
PropertyType = typeof(string)
}),
new SettingsPropertyValue(new SettingsProperty("State")
{
DefaultValue = "TX",
PropertyType = typeof(string)
})
};
usage would be:
var matches = settings.Where<SettingsPropertyValue>(x => x.Name == "City")
alternatively you could use the LINQ Cast<T> operator to query the settings:
var matches = settings.Cast<SettingsPropertyValue>()
.Where(x => x.Name == "City");
if you expect only one possible match then use FirstOrDefault() instead of Where()
var match = settings.Cast<SettingsPropertyValue>()
.FirstOrDefault(x => x.Name == "City");
It's been a while since the question was answered and many things have changed since then.
You could cast the SettingsPropertyValueCollection to a list (or other container) and query it right away.
So, this would be my solution nowadays:
SettingsPropertyValueCollection settings = Properties.Settings.Default.PropertyValues
settings.Cast<SettingsPropertyValue>().ToList().Where(p => p.Name == "myProperty");
I have the following that I'd like to sort:
IQueryable<Map> list;
list = from item in ctx.MAP
.Include("C")
.Include("L")
.Include("L.DP")
select item;
return list.OrderBy(m=>(m.L.DP.Name + m.L.Code));
This works, but it sorts alphabetically - so 12 comes before 9. (Assume Code is a numeric field)
What is the best way to sort this so Code is sorted numerically?
You probably want to use the ThenBy extension method to be able to sort by multiple fields ;)
In your case that would be
return list.OrderBy(m=>m.L.DP.Name).ThenBy(m => m.L.Code);
var results = db.Blogs.AsEnumerable()
.Select(sr => new
{
Searchresult = sr,
Words = Regex.Split(sr.Name, #"[^\S\r\n {1,}").Union(Regex.Split(sr.Name2, #"[^\S\r\n]{1,}"))
})
.OrderByDescending(x => x.Words.Count(w => {
foreach (var item in searchTerms)
{
if(w.ToLower().Contains(item))
{
return true;
}
}
return false;
}))
.Select(x => x.Searchresult);