[英]Put LINQ query result to DataTable
我有這個查詢:
var smallExchangeReport = from ex in exchangeProgReport
where !string.IsNullOrEmpty(ex.comment)
group ex by new { ex.siteName } into g
select new SummuryReportTraffic
{
siteName = g.Key.siteName,
exchangeCounter = g.Where(x => x.Prog1ToProg2Check == 1).Count(),
descriptions = (from t in g
group t by new { t.comment, t.siteName } into grp
select new Description
{
title = grp.Key.comment,
numbers = grp.Select(x => x.comment).Count()
})
};
在某些時候,我使用foreach循環將其放入dataTable中:
foreach (var item in smallExchangeReport)
{
dr = smrTable.NewRow();
foreach (var d in item.descriptions)
{
dr[d.title] = d.numbers;
}
smrTable.Rows.Add(dr);
}
但是我需要在不使用foreach循環的情況下將LINQ結果放入dataTable中。 所以我根據此鏈接對上面的代碼做了一些更改:
DataTable dt = new DataTable();
DataRow dr = dt.NewRow();
IEnumerable<DataRow> smallExchangeReport = from ex in exchangeProgReport.AsEnumerable()
where !string.IsNullOrEmpty(ex.comment)
group ex by new { ex.siteName } into g
select new
{
siteName = g.Key.siteName,
exchangeCounter = g.Where(x => x.Prog1ToProg2Check == 1).Count(),
descriptions = (from t in g.AsEnumerable()
group t by new { t.comment, t.siteName } into grp
select new
{
title = grp.Key.comment,
numbers = grp.Select(x => x.comment).Count()
})
};
// Create a table from the query.
DataTable boundTable = smallExchangeReport.CopyToDataTable<DataRow>();
但是在更改的LINQ查詢上我得到此錯誤:
Cannot implicitly convert type:'System.Collections.Generic.IEnumerable<<anonymous type: string siteName, int exchangeCounter>>' to
'System.Collections.Generic.IEnumerable<System.Data.DataRow>'. An explicit conversion exists (are you missing a cast?)
我的問題是如何強制轉換查詢以使其正常工作?我試圖強制轉換為(DataRow)LINQ的結果,但沒有成功。
在LINQ查詢中,您嘗試獲取IEnumerable<DataRow>
作為結果,但實際上您選擇的是匿名類型的新對象: select new { siteName = .... }
。 這不能工作,因為您的匿名類型不能轉換為DataRow
。
您需要做的是使用將填充DataRow
的函數,如下所示:
DataRow PopulateDataRow(
DataTable table,
string siteName,
int exchangeCounter,
IEnumerable<Description> descriptions
{
var dr = table.NewRow();
// populate siteName and exchangeCounter
// (not sure how your data row is structured, so I leave it to you)
foreach (var d in descriptions)
{
dr[d.title] = d.numbers;
}
return dr;
}
然后在您的LINQ查詢中,如下使用它:
IEnumerable<DataRow> smallExchangeReport =
from ex in exchangeProgReport.AsEnumerable()
where !string.IsNullOrEmpty(ex.comment)
group ex by new { ex.siteName } into g
select PopulateDataRow(
smrTable,
siteName: g.Key.siteName,
exchangeCounter: g.Where(x => x.Prog1ToProg2Check == 1).Count(),
descriptions: (from t in g.AsEnumerable()
group t by new { t.comment, t.siteName } into grp
select new Description {
title = grp.Key.comment,
numbers = grp.Select(x => x.comment).Count()
}
)
);
此解決方案擺脫了一個foreach
(在行上),而留下了另一個(在描述上)。
如果刪除第二個foreach
很重要...我仍將其保留在PopulateDataRow
。 我看不到刪除它的優雅方法。 您可以從LINQ查詢中調用一個方法,該方法的讀取方式像確定性函數,但實際上會產生在數據行上設置列值的副作用,但我覺得不合適。
這可以幫助您。
定義表結構。
DataTable tbl = new DataTable();
tbl.Columns.Add("Id");
tbl.Columns.Add("Name");
並且我們需要從匿名類型創建數據行。
Func<object, DataRow> createRow = (object data) =>
{
var row = tbl.NewRow();
row.ItemArray = data.GetType().GetProperties().Select(a => a.GetValue(data)).ToArray();
return row;
};
用假查詢測試:
var enumarate = Enumerable.Range(0, 10);
var rows = from i in enumarate
select createRow( new { Id = i, Name = Guid.NewGuid().ToString() });
var dataTable = rows.CopyToDataTable<DataRow>();
您可以使用以下方法:
private DataTable ListToDataTable<T>(List<T> objs, string tableName) {
var table = new DataTable(tableName);
var lists = new List<List<object>>();
// init columns
var propertyInfos = new List<PropertyInfo>();
foreach (var propertyInfo in typeof(T).GetProperties()) {
propertyInfos.Add(propertyInfo);
if(propertyInfo.PropertyType.IsEnum || propertyInfo.PropertyType.IsNullableEnum()) {
table.Columns.Add(propertyInfo.Name, typeof(int));
} else {
table.Columns.Add(propertyInfo.Name, Nullable.GetUnderlyingType(propertyInfo.PropertyType) ?? propertyInfo.PropertyType);
}
table.Columns[table.Columns.Count - 1].AllowDBNull = true;
}
// fill rows
foreach(var obj in objs) {
var list = new List<object>();
foreach(var propertyInfo in propertyInfos) {
object currentValue;
if(propertyInfo.PropertyType.IsEnum || propertyInfo.PropertyType.IsNullableEnum()) {
var val = propertyInfo.GetValue(obj);
if(val == null) {
currentValue = DBNull.Value;
} else {
currentValue = (int)propertyInfo.GetValue(obj);
}
} else {
var val = propertyInfo.GetValue(obj);
currentValue = val ?? DBNull.Value;
}
list.Add(currentValue);
}
lists.Add(list);
}
lists.ForEach(x => table.Rows.Add(x.ToArray()));
return table;
}
編輯:
使用此擴展方法:
public static bool IsNullableEnum(this Type t) {
var u = Nullable.GetUnderlyingType(t);
return u != null && u.IsEnum;
}
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