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Object reference not set to an instance of an object in LINQ when using contains


Object reference not set to an instance of an object in LINQ when using contains

By : kaspyre
Date : November 15 2020, 06:54 AM
To fix the issue you can do Since neither db.TableName.Where(n => false).ToList() nor db.TableName.Where(n => true).ToList() produces an exception, the problem must be in the EF data provider for MySql.
Stack trace that you have posted confirms that assumption: the exception happens at the SQL generation stage, before EF even gets to your data.
code :
[NullReferenceException: Object reference not set to an instance of an object.]
   MySql.Data.Entity.SqlGenerator.Visit(DbPropertyExpression expression) +18
   MySql.Data.Entity.SqlGenerator.Visit(DbInExpression expression) +39
   System.Data.Entity.Core.Common.CommandTrees.DbInExpression.Accept(DbExpressionVisitor`1 visitor) +64
   MySql.Data.Entity.SqlGenerator.VisitBinaryExpression(DbExpression left, DbExpression right, String op) +82
   MySql.Data.Entity.SqlGenerator.Visit(DbAndExpression expression) +49
   ...


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Unable to Select in LINQ to XML, error: Object reference not set to an instance of an object

Unable to Select in LINQ to XML, error: Object reference not set to an instance of an object


By : bcorrea2
Date : March 29 2020, 07:55 AM
hope this fix your issue The problem is that you're using the Value property everywhere - that will always fail if the result of foo.Element(...) returns null due to the element being missing. Fortunately, there's a simple way round it - cast to string instead. The XElement explicit conversion to string returns null if the "input" is null, which is very handy.
code :
var query = from c in feed.Descendants("VEHICLES")
            where (string) c.Element("VehicleType") == "0"
            select new
            {
                Vin = (string) c.Element("Vin"),
                Status = (string) c.Element("VehicleType"),
                Year = (string) c.Element("Year")
            };
c# linq select new class Error : Object reference not set to an instance of an object

c# linq select new class Error : Object reference not set to an instance of an object


By : Adnan Al Sousy
Date : March 29 2020, 07:55 AM
I wish did fix the issue. i want to bind gridview with my custom entity whitch i populate from data base but i get error Object reference not set to an instance of an object i know the error is from my gridlink class when select new and want to set to link property in this line : link = { linkName = "tyr", linkSrc = "ytr" }, because when i earase it the error stop and gridview bind thanks , You should be instantiating a gridlink like this:
code :
link = new gridlink { linkName = "tyr", linkSrc = "ytr" },
Object reference not set to an instance of an object error attempting to find an object recursively using LINQ

Object reference not set to an instance of an object error attempting to find an object recursively using LINQ


By : princemanash
Date : March 29 2020, 07:55 AM
hop of those help? You can use either of the following methods to traverse the tree structure recursively:
code :
public static IEnumerable<T> Traverse<T>(IEnumerable<T> source, Func<T, IEnumerable<T>> childSelector)
{
    var queue = new Queue<T>(source);
    while (queue.Any())
    {
        var item = queue.Dequeue();
        yield return item;
        foreach (var child in childSelector(item))
        {
            queue.Enqueue(child);
        }
    }
}

public static IEnumerable<T> Traverse<T>(T root, Func<T, IEnumerable<T>> childSelector)
{
    return Traverse(new[] { root }, childSelector);
}
Category root = new Category();
var searchResult = Traverse(root, item => item.Categories)
            .Where(category => category.Name == "testValue")
            .FirstOrDefault();
Traverse(root, item => item.Categories ?? Enumerable.Empty<Category>())
Unable to read attribute in Linq to xml, error: Object reference not set to an instance of an object

Unable to read attribute in Linq to xml, error: Object reference not set to an instance of an object


By : user69029
Date : March 29 2020, 07:55 AM
Hope this helps I am new in Linq to xml. My xml string is as follows : , You need to get the root element first. Change:
code :
var addParams = from addParam in l_oXDoc.Element("add").Elements("item")
var addParams = from addParam in 
l_oXDoc.Descendants("root").First().Element("add").Elements("item")
Left outer join linq query object reference not set to an instance of an object

Left outer join linq query object reference not set to an instance of an object


By : volkov
Date : March 29 2020, 07:55 AM
like below fixes the issue When you use DefaultIfEmpty, default value is assigned when no matches are found, so you need to check for null and assign proper value, something like this:-
code :
ButtonName = m!= null ? m.ButtonName  : String.Empty
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