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Try within Linq query


Try within Linq query

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Try within Linq query
Tag : chash , By : niel
Date : November 23 2020, 12:01 PM

This might help you try using a scope in the Select() method and a Where() to filter the null outputs:
        var result = ListOfFiles.Select(_s =>
            {
                try
                {
                    return new ObjectA(_s);
                }
                catch (Exception)
                {
                    return null;
                }

            }).Where(x => x != null).ToList();

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LINQ - How to make a linq query with left join, group by, where clause and order by in a single query


Tag : development , By : kameel
Date : March 29 2020, 07:55 AM
This might help you I have googled for four days but not found a single example which contains all three keywords in a single linq query.
Dim query = (From n In tblNseFo.AsEnumerable _
                            Where n!client_id = intClientID _
                            Group Join c In tblClient _
                            On n!client_id Equals c!client_id Into cs = Group _
                            From c In cs.DefaultIfEmpty _
                            Group n, c By _
                            c!client_name, n!instrument_group_id, n!trade_date Into gs = Group _
                            Order By trade_date _
                            Select New With { _
                                .client_name = client_name, _
                                .instrument_group_id = instrument_group_id, _
                                .trade_date = trade_date, _
                                .TotBuyQty = gs.Sum(Function(x) x.n!buy_qty), _
                                .TotSellQty = gs.Sum(Function(x) x.n!sell_qty), _
                                .TotBuyVal = gs.Sum(Function(x) x.n!buy_value) + gs.Sum(Function(x) x.n!buy_brokerage), _
                                .TotSellVal = gs.Sum(Function(x) x.n!sell_value) - gs.Sum(Function(x) x.n!sell_brokerage), _
                                .ProfitLoss = (gs.Sum(Function(x) x.n!sell_value) - gs.Sum(Function(x) x.n!sell_brokerage)) - _
                                              (gs.Sum(Function(x) x.n!buy_value) + gs.Sum(Function(x) x.n!buy_brokerage))})

Some confusion with Linq-to-Objects query operating on results of Linq-to-Entities query


Tag : development , By : Sigfrieg
Date : March 29 2020, 07:55 AM
wish of those help First context.Contacts is processed by the EF query provider which translates expressions (from IQueryable) into SQL.
Then, by AsEnumerable, the link with the EF query provider is broken and anything after that is linq to objects, working on the result set from the preceding statement.

Nesting Linq-to-Objects query within Linq-to-Entities query –what is happening under the covers?


Tag : development , By : Adam
Date : March 29 2020, 07:55 AM
help you fix your problem I've just tried this in LinqPad, and the generated SQL looks like:
-- Region Parameters
DECLARE @p0 Int = 5
DECLARE @p1 Int = 1
-- EndRegion
SELECT [t0].[ContactID], [t0].[Name]
FROM [Contacts] AS [t0]
WHERE ([t0].[ContactID] = @p0) OR ([t0].[ContactID] = @p1)
var numbers = new int[] { 1, 2, 3, 4, 5 };

int max = numbers.Max();
int first = numbers.FirstOrDefault();

var contacts = from c in context.Contacts
   where c.ContactID == max !| c.ContactID == first
   select c;

EntityFramework LINQ query count fails but query returns result. How to optimize LINQ query?


Tag : chash , By : Jarques
Date : March 29 2020, 07:55 AM
This might help you Not quite sure that's the problem, but at least let try to eliminate the potential effect of the so called Parameter Sniffing Problem by eliminating the dateStart / dateEnd parameters by manually building expression with constant values.
First, a little helper method:
using System;
using System.Linq;
using System.Linq.Expressions;

public static class QueryableUtils
{
    public static IQueryable<T> WhereBetween<T>(this IQueryable<T> source, Expression<Func<T, DateTime>> dateSelector, DateTime? startDate, DateTime? endDate)
    {
        if (startDate == null && endDate == null) return source;
        var startCond = startDate != null ? Expression.GreaterThanOrEqual(dateSelector.Body, Expression.Constant(startDate.Value)) : null;
        var endCond = endDate != null ? Expression.LessThanOrEqual(dateSelector.Body, Expression.Constant(endDate.Value)) : null;
        var predicate = Expression.Lambda<Func<T, bool>>(
            startCond == null ? endCond : endCond == null ? startCond : Expression.AndAlso(startCond, endCond),
            dateSelector.Parameters[0]);
        return source.Where(predicate);
    }
}
//if (dateStart.HasValue)
//    query = query.Where(e => e.outer.ValueDate >= dateStart.Value);
//if (dateEnd.HasValue)
//    query = query.Where(e => e.outer.ValueDate <= dateEnd.Value);
query = query.WhereBetween(e => e.outer.ValueDate, dateStart, dateEnd);

linq query insert exist query string into linq query


Tag : chash , By : Yolanda N. Ceron
Date : March 29 2020, 07:55 AM
Does that help I want to make the query follow the query string of the website but it cant be done in this way, is there any other option to do something like this? For example i can insert name,type,class in the query string but not every variable is need to search for the student , try this:
        var query = from c in db.Students select c;
        if (Request.QueryString["Name"] != null)
        {
            name = Request.QueryString["Name"];
            query = query.Where(c => c.name == name);
        }

        if (Request.QueryString["Type"] != null)
        {
            type += Request.QueryString["Type"];
            query = query.Where(c => c.type == type);
        }

        GridView1.DataSource = query.ToList()
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