如何解决Parallel.Foreach SQL查询有时会导致连接
我将重构您的业务逻辑(连接到数据库)。
public class sqlOperation
{
public sqlOperation()
{
Queries = new List<string>();
}
public string TableName { get; set; }
public string ConnectionString { get; set; }
public List<string> Queries { get; set; }
}
public static List<DataTable> GetAllData(IEnumerable<sqlOperation> sql)
{
var taskArray =
sql.SelectMany(s =>
s.Queries
.Select(query =>
Task.Run(() => //Task.Factory.StartNew for .NET 4.0
ExecuteQuery(s.ConnectionString, s.TableName, query))))
.ToArray();
try
{
Task.WaitAll(taskArray);
}
catch(AggregateException e)
{
MessageBox.Show(e.ToString(), "GetAllData error");
}
return taskArray.Where(t => !t.IsFaulted).Select(t => t.Result).ToList();
}
public static DataTable ExecuteQuery(string connectionString, string tableName, string query)
{
DataTable dataTable = null;
using (var connection = new sqlConnection(connectionString))
{
dataTable = new DataTable();
dataTable.TableName = tableName;
using(var command = new sqlCommand(query, connection))
{
connection.open();
using(var adapter = new sqlDataAdapter())
{
adapter.SelectCommand = command;
adapter.Fill(dataTable);
}
}
}
return dataTable;
}
解决方法
我需要加快在应用程序中执行12个查询的速度。我从常规的foreach切换到Parallel.ForEach。但是有时我会收到一条错误消息,提示“
ExecuteReader需要打开且可用的连接。连接的当前状态为连接中”。据我了解,由于12个查询中的许多查询都使用相同的InitialCatalog,因此12个查询中并没有真正的新连接,这可能是问题所在吗?我怎样才能解决这个问题?“
sql”是“ Sql”类型的列表-一个类只是一个字符串名称,字符串connectiona和一个查询列表。这是代码:
/// <summary>
/// Connects to SQL,performs all queries and stores results in a list of DataTables
/// </summary>
/// <returns>List of data tables for each query in the config file</returns>
public List<DataTable> GetAllData()
{
Stopwatch sw = new Stopwatch();
sw.Start();
List<DataTable> data = new List<DataTable>();
List<Sql> sql=new List<Sql>();
Sql one = new Sql();
one.connection = "Data Source=XXX-SQL1;Initial Catalog=XXXDB;Integrated Security=True";
one.name = "Col1";
one.queries.Add("SELECT Name FROM [Reports]");
one.queries.Add("SELECT Other FROM [Reports2]");
sql.Add(one);
Sql two = new Sql();
two.connection = "Data Source=XXX-SQL1;Initial Catalog=XXXDB;Integrated Security=True";
two.name = "Col2";
two.queries.Add("SELECT AlternateName FROM [Reports1]");
sql.Add(two);
Sql three = new Sql();
three.connection = "Data Source=YYY-SQL2;Initial Catalog=YYYDB;Integrated Security=True";
three.name = "Col3";
three.queries.Add("SELECT Frequency FROM Times");
sql.Add(three);
try
{
// ParallelOptions options = new ParallelOptions();
//options.MaxDegreeOfParallelism = 3;
// Parallel.ForEach(sql,options,s =>
Parallel.ForEach(sql,s =>
//foreach (Sql s in sql)
{
foreach (string q in s.queries)
{
using (connection = new SqlConnection(s.connection))
{
connection.Open();
DataTable dt = new DataTable();
dt.TableName = s.name;
command = new SqlCommand(q,connection);
SqlDataAdapter adapter = new SqlDataAdapter();
adapter.SelectCommand = command;
adapter.Fill(dt);
//adapter.Dispose();
lock (data)
{
data.Add(dt);
}
}
}
}
);
}
catch (Exception ex)
{
MessageBox.Show(ex.ToString(),"GetAllData error");
}
sw.Stop();
MessageBox.Show(sw.Elapsed.ToString());
return data;
}
这是我需要的Sql类:
/// <summary>
/// Class defines a SQL connection and its respective queries
/// </summary>
public class Sql
{
/// <summary>
/// Name of the connection/query
/// </summary>
public string name { get; set; }
/// <summary>
/// SQL Connection string
/// </summary>
public string connection { get; set; }
/// <summary>
/// List of SQL queries for a connection
/// </summary>
public List<string> queries = new List<string>();
}
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