使用Asp.Net Core MVC 开发项目实践[第三篇:基于EF Core的扩展]

51core 2019-02-25 原文

上篇我们说到了EFCore的基础使用,这篇我们将讲解下基于EFCore的扩展.

我们在Mango.Framework.EFCore类库项目中创建一个类名EFExtended的扩展类,并且引入相关的命名空间

using System;
using System.Reflection;
using System.Collections.Generic;
using System.Data;
using System.Data.Common;
using System.Data.SqlClient;
using Microsoft.EntityFrameworkCore;
using System.Linq;
using System.Linq.Expressions;
namespace Mango.Framework.EFCore
{
    public static class EFExtended
    {}
}

第一个扩展:基于传统DataTable(这个在2.0中才开始有)的返回

        #region 查询返回DataTable的扩展
        
        ///       ///       ///自定义SQL语句       ///参数       ///       public static DataTable QueryDataTable(this DbContext context, string sql, params SqlParameter[] parameters)
        {
            DbConnection connection = null;
            DbCommand command = null;
            try
            {
                connection = context.Database.GetDbConnection();
                if (connection.State == ConnectionState.Closed)
                {
                    connection.Open();
                }
                command = connection.CreateCommand();
                command.CommandText = sql;
                command.Parameters.AddRange(parameters);
                DbDataReader reader = command.ExecuteReader();
                var result= FillDataTable(reader);
                //释放连接资源
                command.Dispose();
                connection.Close();
                //
                return result;
            }
            catch (Exception ex)
            {
                throw ex;
            }
            finally
            {
                //释放连接资源
                if (command != null)
                {
                    command.Dispose();
                }
                if (connection != null)
                {
                    connection.Close();
                }
            }
        }
        ///       ///       ///       private static DataTable FillDataTable(DbDataReader reader)
        {
            bool defined = false;

            DataTable table = new DataTable();
            
            while (reader.Read())
            {
                object[] values = new object[reader.FieldCount];
                //插入列信息
                if (!defined)
                {
                    for (int i = 0; i < reader.FieldCount; i++)
                    {
                        DataColumn column = new DataColumn()
                        {
                            ColumnName = reader.GetName(i),
                            DataType = reader.GetFieldType(i)
                        };

                        table.Columns.Add(column);
                    }

                    defined = true;
                }

                //插入数据
                reader.GetValues(values);
                DataRow dataRow = table.NewRow();
                for (int i = 0; i < values.Length; i++)
                {
                    dataRow[i] = values[i];
                }
                table.Rows.Add(dataRow);
            }
            return table;
        }
        #endregion

就是通过DbCommand类执行SQL语句返回DbDataReader的数据集合,将返回的数据集合填充到DataTable实例中去.

第二个扩展:基于SQL语句的查询返回指定的集合对象

using System;
using System.Collections.Generic;
using System.Reflection;
using System.ComponentModel;
namespace Mango.Framework.EFCore
{
    public class DbIdentity
    {
        ///       ///       ///       ///       internal static object Change(object value, Type type)
        {
            if (type.IsGenericParameter)
            {
                if (type.IsGenericParameter && type.GetGenericTypeDefinition().Equals(typeof(Nullable<>)))
                {
                    if (value == null)
                    {
                        return null;
                    }
                    NullableConverter nullableConverter = new NullableConverter(type);
                    value = Convert.ChangeType(value, type);
                }
            }
            return value;
        }
    }

}