Entity Framework多视图条件查询、排序

来源：互联网发布：马克斯cms论坛编辑：程序博客网时间：2024/05/22 06:16

Entity Framework在C#中常常用于底层和数据库交互，也就是DAL层。而Entity Framework中与数据库交互时底层与数据库通讯的重要的容器就是DbContext。

而使用DbContext对数据库联表查询是最常见的操作。这里介绍多视图联合查询的加条件，等一些内容

using System;using System.Collections.Generic;using System.Linq;using System.Linq.Expressions;using System.Text;namespace RBIM.COMMON{    public static class PredicateBuilder    {        /// <summary>        /// 机关函数应用True时：单个AND有效，多个AND有效；单个OR无效，多个OR无效；混应时写在AND后的OR有效          /// </summary>        /// <typeparam name="T"></typeparam>        /// <returns></returns>        public static Expression<Func<T, bool>> True<T>() { return f => true; }        /// <summary>        /// 机关函数应用False时：单个AND无效，多个AND无效；单个OR有效，多个OR有效；混应时写在OR后面的AND有效          /// </summary>        /// <typeparam name="T"></typeparam>        /// <returns></returns>        public static Expression<Func<T, bool>> False<T>() { return f => false; }        public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> expr1,                                                            Expression<Func<T, bool>> expr2)        {            var invokedExpr = Expression.Invoke(expr2, expr1.Parameters.Cast<Expression>());            return Expression.Lambda<Func<T, bool>>                  (Expression.Or(expr1.Body, invokedExpr), expr1.Parameters);        }        public static Expression<Func<T, bool>> And<T>(this Expression<Func<T, bool>> expr1,                                                             Expression<Func<T, bool>> expr2)        {            var invokedExpr = Expression.Invoke(expr2, expr1.Parameters.Cast<Expression>());            return Expression.Lambda<Func<T, bool>>                  (Expression.And(expr1.Body, invokedExpr), expr1.Parameters);        }    }}

数据接口实现层:

/// <summary>        ///获取所有数据TransducerConfiguration        /// </summary>        public IList<FindStressDetectionByProjectKey> GetStressDetectionInfoList(Dictionary<string, string> dicparams)        {            try            {                Expression<Func<FindStressDetectionByProjectKey, bool>> searchPredicate = PredicateBuilder.True<FindStressDetectionByProjectKey>();                foreach (string key in dicparams.Keys)                {                    string condition = string.Empty;                    switch (key.ToLower())                    {                        case "projectkey": //case自己扩展                              condition = dicparams[key];                            searchPredicate = searchPredicate.And(c => c.ProjectKey.ToString() == condition);                            break;                        case "smsid":                            condition = dicparams[key];                            searchPredicate = searchPredicate.And(c => c.Smsid == condition);                            break;                        case "tdh":                            condition = dicparams[key];                            searchPredicate = searchPredicate.And(c => c.TDH == condition);                            break;                        default:                            break;                    }                }                return _dbContext.FindStressDetectionByProjectKey.Where(searchPredicate.Compile()).OrderByDescending(c => c.ID).ToList();            }            catch (EntityException e)            {                throw e.InnerException;            } 而UI层调用时:

Dictionary<string, string> dicparams = new Dictionary<string, string>();IList list = HardwareServiceFacade.hardwareService.SoapService.GetStressDetectionInfoList(dicparams).ToList();

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