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Using `System.String Concat` in `LINQ to Entities` generates `CAST`s instead of `CONCAT`


Using `System.String Concat` in `LINQ to Entities` generates `CAST`s instead of `CONCAT`

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Using `System.String Concat` in `LINQ to Entities` generates `CAST`s instead of `CONCAT`
Tag : chash , By : Steven Weber
Date : November 26 2020, 12:01 PM

hop of those help? As I can understand from the docs, when one uses string.Concat from a querying technology, such as LINQ to Entities, this canonical function should be translated to the correct corresponding store function for the provider being used, meaning Concat for MsSQL's T-SQL. But when I'm running the following test code: , So to get things working we won't use LINQ, but DbSet.SqlQuery:
var contains = list.Aggregate(new System.Text.StringBuilder(),
                              (sb, s) => sb.Append($"N'{s}', "),
                              sb => (sb.Length > 0)
                                      ? sb.ToString(0, sb.Length - 2)
                                      : null);
if (contains == null)
{
  //ToDo: list is empty, we've got a problem
}
else
{
  var query = testDB.Items.SqlQuery($@"SELECT [E1].[Id],..
                                     FROM [testDB].[Items] AS [E1]
                                     WHERE CONCAT_WS(':', [E1].[Id],..) IN ({contains })");

}

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Concat the string with linq to entities


Tag : chash , By : user179271
Date : March 29 2020, 07:55 AM
will help you I'm using the Dynamic Linq with Linq to Entities ,
Option 1:
fields.Add("or (LastName + \", \" + MiddleName + \" \" + FirstName).Contains(@1)");
fields.Add("or string.Concat(LastName, \", \", MiddleName, \" \", FirstName).Contains(@1)");
Expression GenerateStringConcat(Expression left, Expression right) {
    return Expression.Call(
        null,
        typeof(string).GetMethod("Concat",
            new[] { typeof(object), typeof(object) }),
        new[] { left, right });
}
Expression GenerateStringConcat(Expression left, Expression right) {
    return Expression.Call(
        null,
        typeof(string).GetMethod("Concat",
            new[] { typeof(string), typeof(string) }),
        new[] { left, right });
}

LINQ to Entities does not recognize the method 'System.String Concat(System.Object)' method,


Tag : chash , By : nseibert
Date : March 29 2020, 07:55 AM
Hope that helps I am getting LINQ to Entities does not recognize the method 'System.String Concat(System.Object)' method, and this method cannot be translated into a store expression. error when I am trying to concatenate number with string in LINQ? how to resolve this? , you can do
SqlFunctions.StringConvert((double)factInitiative.Location_Idx) + ";" + factInitiative.Dim_Location.Location_Name

concat in FSharp.Core.String vs Concat in System.String


Tag : string , By : simonth
Date : March 29 2020, 07:55 AM
To fix the issue you can do I'm not sure that these 2 are equivalent:
FSharp's String.concat is used to join a sequence of strings into a single string with a delimeter:
let strings = [ "tomatoes"; "bananas"; "apples" ]
let fullString = String.concat ", " strings
printfn "%s" fullString
[<CompiledName("Concat")>]
let concat sep (strings : seq<string>) =  
    String.Join(sep, strings)
let concatWithSpace xs = 
  String.concat " " xs

linq to entities skip after concat


Tag : chash , By : jamerson
Date : March 29 2020, 07:55 AM
wish helps you I want to display results that don't have a secondary ID displayed first and then display items that do have a secondary ID. But then I need to Skip and Take. , You can do the job with a single query
result = result
.OrderByDescending(t => (t.second_id== null || t.second_id.Trim() == 
 string.Empty))
.ThenBy(t => t.second_id)
.ThenBy(t => t.first_id)
.Select(t => t.primary_key)
.Skip(pageSize * pageNumber)
.Take(pageSize)
.ToList();

LINQ to Entities .Concat() on two IQueryables throws NullReferencesException


Tag : chash , By : Stephen Judge
Date : March 29 2020, 07:55 AM
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