Refactored for testablility: split SqlTableCreator into two separate testable and mockable classes with interfaces and added an internal constructor to MSSqlServerSinkTraits which allows injection of an ISqlTableCreator.

Author: ckadluba

src/Serilog.Sinks.MSSqlServer/Sinks/MSSqlServer/MSSqlServerSinkTraits.cs

@@ -46,6 +46,21 @@ public MSSqlServerSinkTraits(
             IFormatProvider formatProvider,
             bool autoCreateSqlTable,
             ITextFormatter logEventFormatter)
+            : this(connectionString, tableName, schemaName, columnOptions, formatProvider, autoCreateSqlTable,
+                logEventFormatter, new SqlTableCreator(new SqlCreateTableWriter()))
+        {
+        }
+
+        // Internal constructor with injectable dependencies for better testability
+        internal MSSqlServerSinkTraits(
+            string connectionString,
+            string tableName,
+            string schemaName,
+            ColumnOptions columnOptions,
+            IFormatProvider formatProvider,
+            bool autoCreateSqlTable,
+            ITextFormatter logEventFormatter,
+            ISqlTableCreator sqlTableCreator)
         {
             if (string.IsNullOrWhiteSpace(connectionString))
                 throw new ArgumentNullException(nameof(connectionString));
@@ -80,8 +95,7 @@ public MSSqlServerSinkTraits(
             {
                 try
                 {
-                    SqlTableCreator tableCreator = new SqlTableCreator(ConnectionString, SchemaName, TableName, EventTable, ColumnOptions);
-                    tableCreator.CreateTable(); // return code ignored, 0 = failure?
+                    sqlTableCreator.CreateTable(ConnectionString, SchemaName, TableName, EventTable, ColumnOptions); // return code ignored, 0 = failure?
                 }
                 catch (Exception ex)
                 {

src/Serilog.Sinks.MSSqlServer/Sinks/MSSqlServer/Platform/ISqlCreateTableWriter.cs

@@ -0,0 +1,9 @@
+using System.Data;
+
+namespace Serilog.Sinks.MSSqlServer.Platform
+{
+    internal interface ISqlCreateTableWriter
+    {
+        string GetSqlFromDataTable(string schemaName, string tableName, DataTable dataTable, ColumnOptions columnOptions);
+    }
+}

src/Serilog.Sinks.MSSqlServer/Sinks/MSSqlServer/Platform/ISqlTableCreator.cs

@@ -0,0 +1,9 @@
+using System.Data;
+
+namespace Serilog.Sinks.MSSqlServer.Platform
+{
+    internal interface ISqlTableCreator
+    {
+        int CreateTable(string connectionString, string schemaName, string tableName, DataTable dataTable, ColumnOptions columnOptions);
+    }
+}

src/Serilog.Sinks.MSSqlServer/Sinks/MSSqlServer/Platform/SqlCreateTableWriter.cs

@@ -0,0 +1,85 @@
+using System.Data;
+using System.Text;
+
+namespace Serilog.Sinks.MSSqlServer.Platform
+{
+    internal class SqlCreateTableWriter : ISqlCreateTableWriter
+    {
+        public string GetSqlFromDataTable(string schemaName, string tableName, DataTable dataTable, ColumnOptions columnOptions)
+        {
+            var sql = new StringBuilder();
+            var ix = new StringBuilder();
+            int indexCount = 1;
+
+            // start schema check and DDL (wrap in EXEC to make a separate batch)
+            sql.AppendLine($"IF(NOT EXISTS(SELECT * FROM sys.schemas WHERE name = '{schemaName}'))");
+            sql.AppendLine("BEGIN");
+            sql.AppendLine($"EXEC('CREATE SCHEMA [{schemaName}] AUTHORIZATION [dbo]')");
+            sql.AppendLine("END");
+
+            // start table-creatin batch and DDL
+            sql.AppendLine($"IF NOT EXISTS (SELECT s.name, t.name FROM sys.tables t JOIN sys.schemas s ON t.schema_id = s.schema_id WHERE s.name = '{schemaName}' AND t.name = '{tableName}')");
+            sql.AppendLine("BEGIN");
+            sql.AppendLine($"CREATE TABLE [{schemaName}].[{tableName}] ( ");
+
+            // build column list
+            int i = 1;
+            foreach (DataColumn column in dataTable.Columns)
+            {
+                var common = (SqlColumn)column.ExtendedProperties["SqlColumn"];
+
+                sql.Append(GetColumnDDL(common));
+                if (dataTable.Columns.Count > i++) sql.Append(",");
+                sql.AppendLine();
+
+                // collect non-PK indexes for separate output after the table DDL
+                if (common != null && common.NonClusteredIndex && common != columnOptions.PrimaryKey)
+                    ix.AppendLine($"CREATE NONCLUSTERED INDEX [IX{indexCount++}_{tableName}] ON [{schemaName}].[{tableName}] ([{common.ColumnName}]);");
+            }
+
+            // primary key constraint at the end of the table DDL
+            if (columnOptions.PrimaryKey != null)
+            {
+                var clustering = (columnOptions.PrimaryKey.NonClusteredIndex ? "NON" : string.Empty);
+                sql.AppendLine($" CONSTRAINT [PK_{tableName}] PRIMARY KEY {clustering}CLUSTERED ([{columnOptions.PrimaryKey.ColumnName}])");
+            }
+
+            // end of CREATE TABLE
+            sql.AppendLine(");");
+
+            // CCI is output separately after table DDL
+            if (columnOptions.ClusteredColumnstoreIndex)
+                sql.AppendLine($"CREATE CLUSTERED COLUMNSTORE INDEX [CCI_{tableName}] ON [{schemaName}].[{tableName}]");
+
+            // output any extra non-clustered indexes
+            sql.Append(ix);
+
+            // end of batch
+            sql.AppendLine("END");
+
+            return sql.ToString();
+        }
+
+        // Examples of possible output:
+        // [Id] BIGINT IDENTITY(1,1) NOT NULL
+        // [Message] VARCHAR(1024) NULL
+        private string GetColumnDDL(SqlColumn column)
+        {
+            var sb = new StringBuilder();
+
+            sb.Append($"[{column.ColumnName}] ");
+
+            sb.Append(column.DataType.ToString().ToUpperInvariant());
+
+            if (SqlDataTypes.DataLengthRequired.Contains(column.DataType))
+                sb.Append("(").Append(column.DataLength == -1 ? "MAX" : column.DataLength.ToString()).Append(")");
+
+            if (column.StandardColumnIdentifier == StandardColumn.Id)
+                sb.Append(" IDENTITY(1,1)");
+
+            sb.Append(column.AllowNull ? " NULL" : " NOT NULL");
+
+            return sb.ToString();
+        }
+    }
+}

src/Serilog.Sinks.MSSqlServer/Sinks/MSSqlServer/Platform/SqlTableCreator.cs

@@ -1,31 +1,22 @@
 using System.Data;
 using System.Data.SqlClient;
-using System.Text;
 
 namespace Serilog.Sinks.MSSqlServer.Platform
 {
-    internal class SqlTableCreator
+    internal class SqlTableCreator : ISqlTableCreator
     {
-        private readonly string _connectionString;
-        private readonly string _schemaName;
-        private readonly string _tableName;
-        private readonly DataTable _dataTable;
-        private readonly ColumnOptions _columnOptions;
+        private readonly ISqlCreateTableWriter _sqlCreateTableWriter;
 
-        public SqlTableCreator(string connectionString, string schemaName, string tableName, DataTable dataTable, ColumnOptions columnOptions)
+        public SqlTableCreator(ISqlCreateTableWriter sqlCreateTableWriter)
         {
-            _connectionString = connectionString;
-            _schemaName = schemaName;
-            _tableName = tableName;
-            _dataTable = dataTable;
-            _columnOptions = columnOptions;
+            _sqlCreateTableWriter = sqlCreateTableWriter;
         }
 
-        public int CreateTable()
+        public int CreateTable(string connectionString, string schemaName, string tableName, DataTable dataTable, ColumnOptions columnOptions)
         {
-            using (var conn = new SqlConnection(_connectionString))
+            using (var conn = new SqlConnection(connectionString))
             {
-                string sql = GetSqlFromDataTable();
+                string sql = _sqlCreateTableWriter.GetSqlFromDataTable(schemaName, tableName, dataTable, columnOptions);
                 using (SqlCommand cmd = new SqlCommand(sql, conn))
                 {
                     conn.Open();
@@ -34,84 +25,5 @@ public int CreateTable()
 
             }
         }
-
-        private string GetSqlFromDataTable()
-        {
-            var sql = new StringBuilder();
-            var ix = new StringBuilder();
-            int indexCount = 1;
-
-            // start schema check and DDL (wrap in EXEC to make a separate batch)
-            sql.AppendLine($"IF(NOT EXISTS(SELECT * FROM sys.schemas WHERE name = '{_schemaName}'))");
-            sql.AppendLine("BEGIN");
-            sql.AppendLine($"EXEC('CREATE SCHEMA [{_schemaName}] AUTHORIZATION [dbo]')");
-            sql.AppendLine("END");
-
-            // start table-creatin batch and DDL
-            sql.AppendLine($"IF NOT EXISTS (SELECT s.name, t.name FROM sys.tables t JOIN sys.schemas s ON t.schema_id = s.schema_id WHERE s.name = '{_schemaName}' AND t.name = '{_tableName}')");
-            sql.AppendLine("BEGIN");
-            sql.AppendLine($"CREATE TABLE [{_schemaName}].[{_tableName}] ( ");
-
-            // build column list
-            int i = 1;
-            foreach (DataColumn column in _dataTable.Columns)
-            {
-                var common = (SqlColumn)column.ExtendedProperties["SqlColumn"];
-
-                sql.Append(GetColumnDDL(common));
-                if (_dataTable.Columns.Count > i++) sql.Append(",");
-                sql.AppendLine();
-
-                // collect non-PK indexes for separate output after the table DDL
-                if(common != null && common.NonClusteredIndex && common != _columnOptions.PrimaryKey)
-                    ix.AppendLine($"CREATE NONCLUSTERED INDEX [IX{indexCount++}_{_tableName}] ON [{_schemaName}].[{_tableName}] ([{common.ColumnName}]);");
-            }
-
-            // primary key constraint at the end of the table DDL
-            if (_columnOptions.PrimaryKey != null)
-            {
-                var clustering = (_columnOptions.PrimaryKey.NonClusteredIndex ? "NON" : string.Empty);
-                sql.AppendLine($" CONSTRAINT [PK_{_tableName}] PRIMARY KEY {clustering}CLUSTERED ([{_columnOptions.PrimaryKey.ColumnName}])");
-            }
-
-            // end of CREATE TABLE
-            sql.AppendLine(");");
-
-            // CCI is output separately after table DDL
-            if (_columnOptions.ClusteredColumnstoreIndex)
-                sql.AppendLine($"CREATE CLUSTERED COLUMNSTORE INDEX [CCI_{_tableName}] ON [{_schemaName}].[{_tableName}]");
-
-            // output any extra non-clustered indexes
-            sql.Append(ix);
-
-            // end of batch
-            sql.AppendLine("END");
-
-            return sql.ToString();
-        }
-
-        // Examples of possible output:
-        // [Id] BIGINT IDENTITY(1,1) NOT NULL
-        // [Message] VARCHAR(1024) NULL
-        private string GetColumnDDL(SqlColumn column)
-        {
-            var sb = new StringBuilder();
-
-            sb.Append($"[{column.ColumnName}] ");
-
-            sb.Append(column.DataType.ToString().ToUpperInvariant());
-
-            if (SqlDataTypes.DataLengthRequired.Contains(column.DataType))
-                sb.Append("(").Append(column.DataLength == -1 ? "MAX" : column.DataLength.ToString()).Append(")");
-
-            if (column.StandardColumnIdentifier == StandardColumn.Id)
-                sb.Append(" IDENTITY(1,1)");
-
-            sb.Append(column.AllowNull ? " NULL" : " NOT NULL");
-
-            return sb.ToString();
-        }
-
     }
-
 }