【C#】Linqラムダ式事例集

データがあるかチェックする

C#

String searchAuthor = "John Grisham";
bool contains = tbl.AsEnumerable()
               .Any(row => searchAuthor == row.Field<String>("Author"));

同じ意味

C#

DataRow[] foundAuthors = tbl.Select("Author = '" + searchAuthor + "'");
if(foundAuthors.Length != 0)
{
    // do something...
}

indexの列を追加する

C#

var result =  query.AsEnumerable().Select((x, index) => new { index,x.Id,x.FirstName});

同じ意味

C#

int i = 1;
    var query = from u in dbReport.Users
                join p in dbReport.Physicans on u equals p.User
                let Rank = i++
                select new 
                {
                    Rank.ToString(),
                    u.Id,
                    u.FirstName,
                    ...
                };

where句の複数指定

C#

TotalEatin = Data.kassaOrders.AsEnumerable().Where(x => x.Field<bool>("btwticket") && !x.Field<bool>("terugname") && !x.Field<bool>("teruggenomen"))
    .SelectMany(x => Data.orderDetails.AsEnumerable().Where(d => d.Field<int>("orderid") == x.Field<int>("serial") && !d.Field<bool>("takeout")))
    .Sum(x => x.Field<decimal>("price"));

TotalEatin += Data.kassaOrders.AsEnumerable().Where(x => x.Field<bool>("btwticket") && !x.Field<bool>("terugname") && !x.Field<bool>("teruggenomen"))
    .SelectMany(x => Data.orderDetails.AsEnumerable().Where(d => d.Field<int>("orderid") == x.Field<int>("serial") && !d.Field<bool>("takeout")))
    .SelectMany(x => Data.MenuDetails.AsEnumerable().Where(d => d.Field<int>("orderid") == x.Field<int>("orderid")))
    .Sum(x => x.Field<decimal>("prijs"));

データの更新

C#

var dt = new System.Data.DataTable("tmp");

dt.Columns.Add("col1", typeof(string));
dt.Columns.Add("col2", typeof(string));

var row = dt.NewRow();
row["col1"] = "A01";
row["col2"] = "B01";
dt.Rows.Add(row);

row = dt.NewRow();
row["col1"] = "A02";
row["col2"] = "B02";
dt.Rows.Add(row);

row = dt.NewRow();
row["col1"] = "A03";
row["col2"] = "B03";
dt.Rows.Add(row);

dt.AsEnumerable().Where(r => r.Field<string>("col1") == "A02").Select(r => r["col2"] = "hoge").ToList();