Question

Morning i would like to include a group by in this linq statement, Some records i have being brought back have multiple entries so i need to group them by the productAsin. so i dont have duplicates in my table.

 var query = from a in dc.aProducts
                        join t in dc.tProducts on a.sku equals t.sku
                        join lp in dc.LowestPrices on a.asin equals lp.productAsin
                        orderby t.title
                        select new GetLowestPrices
                        {
                            productAsin = lp.productAsin,
                            sku = t.sku,
                            title = t.title,
                            tweprice = Convert.ToString(t.twePrice),
                            lowprice = Convert.ToString(lp.price),
                            amzprice = Convert.ToString(lp.tweAmzPrice),
                            lastupdated = Convert.ToDateTime(lp.priceDate)
                        };
            return query.ToList();

many thanks in advance.

Answer 1

Use GroupBy Extension method:

  var query = from a in dc.aProducts
                            join t in dc.tProducts on a.sku equals t.sku
                            join lp in dc.LowestPrices on a.asin equals lp.productAsin
                            orderby t.title
                            select new GetLowestPrices
                            {
                                productAsin = lp.productAsin,
                                sku = t.sku,
                                title = t.title,
                                tweprice = Convert.ToString(t.twePrice),
                                lowprice = Convert.ToString(lp.price),
                                amzprice = Convert.ToString(lp.tweAmzPrice),
                                lastupdated = Convert.ToDateTime(lp.priceDate)
                            };

    var groupedData = query.GroupBy(d => d.productAsin);
                return groupedData;

After that you can access that group values and put some aggregate function on them as below:

var groupedData = query.GroupBy(d => d.productAsin).Select( data => new {
productAsin = data.Key,
LowPriceSum = data.Sum(s => Convert.ToInt32(s.price))
}).ToList();

Ref:
group clause (C# Reference)
How to Use LINQ GroupBy