refactor built query with less mem allocation.

AsbCloudDb/EFExtentions.cs

@@ -13,7 +13,7 @@ namespace AsbCloudDb
     {
         static Dictionary<Type, IQueryStringFactory> QueryFactories { get; set; } = new Dictionary<Type, IQueryStringFactory>();
 
-        static IQueryStringFactory GetQueryStringFactory<T>(DbSet<T> dbset)
+        static QueryStringFactory<T> GetQueryStringFactory<T>(DbSet<T> dbset)
             where T : class
         {
             var t = typeof(T);
@@ -30,8 +30,9 @@ namespace AsbCloudDb
         public static Task<int> ExecInsertOrUpdateAsync<T>(this Microsoft.EntityFrameworkCore.Infrastructure.DatabaseFacade database, DbSet<T> dbset, IEnumerable<T> items, CancellationToken token)
             where T : class
         {
-            var factory = (QueryStringFactory<T>)GetQueryStringFactory(dbset);
+            var factory = GetQueryStringFactory(dbset);
             var query = factory.MakeInsertOrUpdateSql(items);
+
             return database.ExecuteSqlRawAsync(query, token);
         }
     }
@@ -41,10 +42,11 @@ namespace AsbCloudDb
     class QueryStringFactory<T> : IQueryStringFactory
         where T : class
     {
+        private readonly string insertHeader;
+
         private readonly string pk;
         private readonly string tableName;
-        private readonly string colunmsString;
+        private readonly string conflictBody;
-        private readonly string conflictUpdateSet;
         private readonly IEnumerable<IClrPropertyGetter> getters;
 
         public QueryStringFactory(DbSet<T> dbset)
@@ -56,8 +58,11 @@ namespace AsbCloudDb
             tableName = dbset.EntityType.GetTableName();
             getters = ps.Select(p => p.GetGetter());
             var colNames = ps.Select(p => $"\"{p.GetColumnBaseName()}\"");
-            colunmsString = $"({string.Join(", ", colNames)})";
+            var colunmsString = $"({string.Join(", ", colNames)})";
-            conflictUpdateSet = string.Join(", ", colNames.Select(n => $"{n} = excluded.{n}"));
+
+            insertHeader = $"INSERT INTO {tableName} {colunmsString} VALUES ";
+            var excludedUpdateSet = string.Join(", ", colNames.Select(n => $"{n} = excluded.{n}"));
+            conflictBody = $" ON CONFLICT {pk} DO UPDATE SET {excludedUpdateSet};";
         }
 
         public string MakeInsertOrUpdateSql(IEnumerable<T> items)
@@ -69,37 +74,35 @@ namespace AsbCloudDb
                   SET column_1 = excluded.column_1, 
                       column_2 = excluded.column_2;
              */
-            var sqlBuilder = new StringBuilder("INSERT INTO ", 7);
+            var builder = new StringBuilder(insertHeader, 7);
-            sqlBuilder.Append(tableName);
+            BuildRows(builder, items);
-            sqlBuilder.Append(colunmsString);
-            sqlBuilder.AppendLine(" VALUES ");
-            sqlBuilder.Append(MakeQueryValues(items));
-            sqlBuilder.AppendLine(" ON CONFLICT ");
             if (string.IsNullOrEmpty(pk))
-            {
+                builder.Append(" ON CONFLICT DO NOTHING;");
-                sqlBuilder.Append("DO NOTHING;");
-            }
             else
+                builder.AppendLine(conflictBody);
+
+            return builder.ToString();
+        }
+
+        private StringBuilder BuildRows(StringBuilder builder, IEnumerable<T> items)
         {
-                sqlBuilder.Append(pk);
+            var list = items.ToList();
-                sqlBuilder.Append(" DO UPDATE SET ");
+            for (int i = 0; i < list.Count; i++)
-                sqlBuilder.AppendLine(conflictUpdateSet);
-                sqlBuilder.Append(';');
-            }
-
-            return sqlBuilder.ToString();
-        }
-
-        private string MakeQueryValues(IEnumerable<T> items)
             {
-            var rows = items.Select(item => MakeRow(item));
+                if(i > 0)
-            return string.Join(",", rows);
+                    builder.Append(',');
+                BuildRow(builder, list[i]);
+            }            
+            return builder;
         }
 
-        private string MakeRow(T item)
+        private StringBuilder BuildRow(StringBuilder builder, T item)
         {
             var values = getters.Select(getter => FormatValue(getter.GetClrValue(item)));
-            return $"({string.Join(",", values)})";
+            builder.Append('(');
+            builder.AppendJoin(",", values);
+            builder.Append(')');
+            return builder;
         }
 
         private static string FormatValue(object v)

ConsoleApp1/Program.cs

@@ -19,6 +19,26 @@ namespace ConsoleApp1
     {
         static void Main(/*string[] args*/)
         {
+            //var options = new DbContextOptionsBuilder<AsbCloudDbContext>()
+            //    .UseNpgsql("Host=localhost;Database=postgres;Username=postgres;Password=q;Persist Security Info=True")
+            //    .Options;
+            //var context = new AsbCloudDbContext(options);
+
+            //var sett = context.Set<TelemetryDataSaub>();
+            //var r = context.Database.ExecInsertOrUpdateAsync(sett, new List<TelemetryDataSaub> { 
+            //    new TelemetryDataSaub
+            //    {
+            //        Date = DateTime.Now,
+            //        IdTelemetry = 3,
+            //        AxialLoad = 100.1f,
+            //    },
+            //    new TelemetryDataSaub
+            //    {
+            //        Date = DateTime.Now.AddSeconds(2),
+            //        IdTelemetry = 3,
+            //        AxialLoad = 100.2f,
+            //    },
+            //}, System.Threading.CancellationToken.None).Result;
             Console.ReadKey(); 
         }
     }