关于c＃：全外连接，在2个数据表上，带有列列表

Full outer join, on 2 data tables, with a list of columns

我有两个数据表，我不知道它们的数据列列表。此列表必须在运行时提取，并用于完整的外部联接。

使用这些列时，需要合并两个表之间的列，并且需要显示所有数据。

到现在为止我所做的是

使用Intersect获取公共列，并实现IEqualityComparer

使用这些列创建一个新的数据表，以便将两个数据表合并到此新表中

但是，我在第二步遇到了与Linq有关的问题。

到目前为止，我有：

获取公用列

1 2	// Get common columns var commonColumns = dt1.Columns.OfType().Intersect(dt2.Columns.OfType(), new DataColumnComparer());

创建新数据表

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// Create the result which is going to be sent to the user
DataTable result = new DataTable();

// Add all the columns from both tables
result.Columns.AddRange(
dt1.Columns.OfType()
.Union(dt2.Columns.OfType(), new DataColumnComparer())
.Select(c => new DataColumn(c.Caption, c.DataType, c.Expression, c.ColumnMapping)).ToArray());

如何从运行时提取的数据列列表中动态获取有效的完整外部联接？

这可能对你有用

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var commonColumns = dt1.Columns.OfType<DataColumn>().Intersect(dt2.Columns.OfType<DataColumn>(), new DataColumnComparer());
DataTable result = new DataTable();

dt1.PrimaryKey = commonColumns.ToArray();

result.Merge(dt1, false, MissingSchemaAction.AddWithKey);
result.Merge(dt2, false, MissingSchemaAction.AddWithKey);

相关讨论

基于Matthew的答案，我创建了一个接受2个以上数据表的函数。我希望它有助于：

用途：

1	var table123 = FullOuterJoinDataTables(table1, table2, table3);

以下是函数源：

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public DataTable FullOuterJoinDataTables(params DataTable[] datatables) // supports as many datatables as you need.
{
DataTable result = datatables.First().Clone();

var commonColumns = result.Columns.OfType<DataColumn>();

foreach (var dt in datatables.Skip(1))
{
commonColumns = commonColumns.Intersect(dt.Columns.OfType<DataColumn>(), new DataColumnComparer());
}

result.PrimaryKey = commonColumns.ToArray();

foreach (var dt in datatables)
{
result.Merge(dt, false, MissingSchemaAction.AddWithKey);
}

return result;
}

/* also create this class */
public class DataColumnComparer : IEqualityComparer<DataColumn>
{
public bool Equals(DataColumn x, DataColumn y) => x.Caption == y.Caption;

public int GetHashCode(DataColumn obj) => obj.Caption.GetHashCode();
}

我也很难得到答案，我正在复制粘贴整个代码。我相信这对你有帮助。

您只需要执行此联接的两个表中的DataTable1、DataTable2和primarykeys即可。可以将DataTable主键设置为

1	datatable1.PrimaryKey = new DataColumn[] { captureDT.Columns["Your Key Name"] };

/ /您的代码

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/// <summary>
/// Combines the data of two data table into a single data table. The grouping of tables
/// will be based on the primary key provided for both the tables.
/// </summary>
/// <param name="table1"></param>
/// <param name="table2"></param>
/// <param name="table1PrimaryKey"></param>
/// <param name="table2PrimaryKey"></param>
/// <returns></returns>
private DataTable DataTablesOuterJoin(DataTable table1, DataTable table2, string table1PrimaryKey, string table2PrimaryKey)
{
DataTable flatDataTable = new DataTable();

foreach (DataColumn column in table2.Columns)
{
flatDataTable.Columns.Add(new DataColumn(column.ToString()));
}
foreach (DataColumn column in table1.Columns)
{
flatDataTable.Columns.Add(new DataColumn(column.ToString()));
}

// Retrun empty table with required columns to generate empty extract
if (table1.Rows.Count <= 0 && table2.Rows.Count <= 0)
{
flatDataTable.Columns.Remove(table2PrimaryKey);
return flatDataTable;
}

var dataBaseTable2 = table2.AsEnumerable();
var groupDataT2toT1 = dataBaseTable2.GroupJoin(table1.AsEnumerable(),
br => new { id = br.Field<string>(table2PrimaryKey).Trim().ToLower() },
jr => new { id = jr.Field<string>(table1PrimaryKey).Trim().ToLower() },
(baseRow, joinRow) => joinRow.DefaultIfEmpty()
.Select(row => new
{
flatRow = baseRow.ItemArray.Concat((row == null) ? new object[table1.Columns.Count] :
row.ItemArray).ToArray()
})).SelectMany(s => s);

var dataBaseTable1 = table1.AsEnumerable();
var groupDataT1toT2 = dataBaseTable1.GroupJoin(table2.Select(),
br => new { id = br.Field<string>(table1PrimaryKey).Trim().ToLower() },
jr => new { id = jr.Field<string>(table2PrimaryKey).Trim().ToLower() },
(baseRow, joinRow) => joinRow.DefaultIfEmpty()
.Select(row => new
{
flatRow = (row == null) ? new object[table2.Columns.Count].ToArray().Concat(baseRow.ItemArray).ToArray() :
row.ItemArray.Concat(baseRow.ItemArray).ToArray()
})).SelectMany(s => s);

// Get the union of both group data to single set
groupDataT2toT1 = groupDataT2toT1.Union(groupDataT1toT2);

// Load the grouped data to newly created table
foreach (var result in groupDataT2toT1)
{
flatDataTable.LoadDataRow(result.flatRow, false);
}

// Get the distinct rows only
IEnumerable rows = flatDataTable.Select().Distinct(DataRowComparer.Default);

// Create a new distinct table with same structure as flatDataTable
DataTable distinctFlatDataTable = flatDataTable.Clone();
distinctFlatDataTable.Rows.Clear();

// Push all the rows into distinct table.
// Note: There will be two different columns for primary key1 and primary key2. In grouped rows,
// primary key1 or primary key2 can have empty values. So copy all the primary key2 values to
// primary key1 only if primary key1 value is empty and then delete the primary key2. So at last
// we will get only one perimary key. Please make sure the non-deleted key must be present in
foreach (DataRow row in rows)
{
if (string.IsNullOrEmpty(row[table1PrimaryKey].ToString()))
row[table1PrimaryKey] = row[table2PrimaryKey];

if (string.IsNullOrEmpty(row[CaptureBusDateColumn].ToString()))
row[CaptureBusDateColumn] = _businessDate;

if (string.IsNullOrEmpty(row[CaptureUserIDColumn].ToString()))
row[CaptureUserIDColumn] = row[StatsUserIDColumn];

distinctFlatDataTable.ImportRow(row);
}

// Sort the table based on primary key.
DataTable sortedFinaltable = (from orderRow in distinctFlatDataTable.AsEnumerable()
orderby orderRow.Field<string>(table1PrimaryKey)
select orderRow).CopyToDataTable();

// Remove primary key2 as we have already copied it to primary key1
sortedFinaltable.Columns.Remove(table2PrimaryKey);

return ReplaceNulls(sortedFinaltable,"0");
}

/// <summary>
/// Replace all the null values from data table with specified string
/// </summary>
/// <param name="dt"></param>
/// <param name="replaceStr"></param>
/// <returns></returns>
private DataTable ReplaceNulls(DataTable dt, string replaceStr)
{
for (int a = 0; a < dt.Rows.Count; a++)
{
for (int i = 0; i < dt.Columns.Count; i++)
{
if (dt.Rows[a][i] == DBNull.Value)
{
dt.Rows[a][i] = replaceStr;
}
}
}
return dt;
}