Accessing Inserted Records Before SubmitChanges() in LINQ to SQL
When working with LINQ to SQL and performing batch insert operations, you might need to access the properties of the newly inserted records before calling SubmitChanges(). Standard LINQ to SQL queries against the Table<T> will only reflect the data that has been persisted to the database.
To address this, you can utilize the following extension methods that allow you to query both the existing records in the table and the records that are currently in the insert cache of the DataContext (i.e., those that have been added but not yet submitted to the database).
Here are the extension methods:
public static List<T> WhereOrInserted<T>(this Table<T> table, Expression<Func<T, bool>> predicate)
where T : class
{
var result = table.Where(predicate).ToList();
if (result != null && result.Count != 0)
return result;
result = table.Context.GetChangeSet().Inserts.Where(a => a.GetType() == typeof(T))
.Select(a => a as T)
.ToList();
return result;
}
public static T FirstOrInserted<T>(this Table<T> table, Expression<Func<T, bool>> predicate)
where T : class
{
var result = table.First(predicate);
if (result != null)
return result;
result = table.Context.GetChangeSet().Inserts.Where(a => a.GetType() == typeof(T))
.Select(a => a as T)
.First();
return result;
}
public static T FirstOrDefaultOrInserted<T>(this Table<T> table, Expression<Func<T, bool>> predicate)
where T : class
{
var result = table.FirstOrDefault(predicate);
if (result != null)
return result;
result = table.Context.GetChangeSet().Inserts.Where(a => a.GetType() == typeof(T))
.Select(a => a as T)
.FirstOrDefault();
return result;
}
How it Works:
The WhereOrInserted method first attempts to retrieve records from the table that match the provided predicate. If no matching records are found in the database, it then checks the Insert collection within the DataContext's change set for any inserted entities of the specified type T that satisfy the predicate.
The FirstOrInserted and FirstOrDefaultOrInserted methods function similarly to the standard First() and FirstOrDefault() methods, but they also examine the insert cache if no matching records are found in the database.
Usage:
To utilize these extension methods, simply call them on your Table<T> instance, just as you would with the standard LINQ methods. These methods enable you to access newly inserted objects before they are actually saved to the database using SubmitChanges().
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