How to Perform a Full Outer Join in LINQ to Merge Two Lists of People Based on ID?

linq -all external connection

Question:

Give two lists of personnel containing IDs and names or surnames, and perform a full external connection to generate a personal list containing names and surnames.

Answer:

The difference between the whole external connection and other connections is that it contains the items from two input lists, even if there is no matching element in another list. For this reason, we can use the extension method, and its working principle is as follows:

Use the specified key selectioner function to create a search table for two input lists.

FullOuterJoin Identify the unique button in the two search tables and combine them into a collection.

traversing key sets and retrieve the corresponding value for each key.
Use the projection function to generate the required results of each iteration.
3. The updated code implementation:

Example usage:

This code will output the following results:

internal static class MyExtensions
{
    internal static IEnumerable<TResult> FullOuterJoin<TA, TB, TKey, TResult>(
        this IEnumerable<TA> a,
        IEnumerable<TB> b,
        Func<TA, TKey> selectKeyA,
        Func<TB, TKey> selectKeyB,
        Func<TA, TB, TKey, TResult> projection,
        IEqualityComparer<TKey> cmp = null)
    {
        cmp = cmp ?? EqualityComparer<TKey>.Default;
        var alookup = a.ToLookup(selectKeyA, cmp);
        var blookup = b.ToLookup(selectKeyB, cmp);

        var keys = new HashSet<TKey>(alookup.Select(p => p.Key), cmp);
        keys.UnionWith(blookup.Select(p => p.Key));

        var join = from key in keys
                   let xa = alookup[key].DefaultIfEmpty(default(TA))
                   let xb = blookup[key].DefaultIfEmpty(default(TB))
                   select projection(xa.FirstOrDefault(), xb.FirstOrDefault(), key);

        return join;
    }
}

This Revised Answer Uses To handle the portal null values ​​from

More GraceFully and Directly Outputs the name and Surname, , Making The Result Clearer. The

var ax = new[] {
    new { id = 1, name = "John" },
    new { id = 2, name = "Sue" } };
var bx = new[] {
    new { id = 1, surname = "Doe" },
    new { id = 3, surname = "Smith" } };

ax.FullOuterJoin(bx, a => a.id, b => b.id, (a, b, id) => new { a?.name, b?.surname, id })
    .ToList().ForEach(Console.WriteLine);

Null-Conditional Operator Prevents Exceptions if Or

Are Null.

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