资讯评论 - 强大的 Lambda 式转 Sql 类库 - SqlSugar 隐藏功能之 Lambda - OSCHINA

使用场景

1、Lambda to sql 一直是ORM中最难的功能之一，如果有现成的解析库那么自已写一个ORM难度将大大降低

2、通过Lambda作为KEY进行缓存操作，特别是仓储模式想要拿到表达式进行通用查询缓存则需要用到表达式解析

3、学习爱好者，如果能够较深入的理Lambda如何去解成Sql，那么你对Lambda的理解将会更上一个层次，而不仅仅在使用上

优点

SqlSugar除了有自带的ORM功能，还是一款强大的拉姆达解析器，并且是市场上独有的拉姆达转Sql类库

SqlSugar不仅小巧并且性能非常的好，毫不逊色于Dapper 甚至更加的优秀，至于性能别看其他人的测评非常不靠谱，自个用了才知道，自个测了才知道

1、高性能表达式解析速度远超EF

2、功能非常完整，并且是产品级的解析类库，支持各种模式的解析

3、小巧你只要引用SqlSugar一个DLL就能使用解析各种数据库、支持Sql函数、支持常用原生函数

安装

.NET CORE / NET5 Nuget SqlSugarCore

.NET 4.5 Nuget SqlSugar

.NET 4.0 Nuget SqlSuagr 4.x

入门

我们先来看一下例子：

static void Main(string[] args)
{
 var age = 11;
 Expression<Func<Test, bool>> exp = a => a.id == age; //表达式
 SqlServerExpressionContext expContext = new SqlServerExpressionContext();//创建解析对象
 expContext.Resolve(exp, ResolveExpressType.WhereSingle);//开始解析
 var value = expContext.Result.GetString();//( [id] = @id0 )
 var pars = expContext.Parameters;// @id:11
}

下面是调试结果：

通过上面的例子就能够完美的将表达式转换成Sql语句

教程案例

1、如何创建 ExpressionContext 解析对象

我们可以通过SqlSugar.DbType进行区分数据库并且进行实例化

ExpressionContext expContext=null;
switch (dbtype)
{
case DbType.MySql:
expContext = new MySqlExpressionContext();
break;
case DbType.SqlServer:
expContext = new SqlServerExpressionContext();
break;
case DbType.Sqlite:
expContext = new SqliteExpressionContext();
break;
case DbType.Oracle:
expContext = new OracleExpressionContext();
break;
case DbType.PostgreSQL:
expContext = new PostgreSQLExpressionContext();
break;
case DbType.Dm:
expContext = new DmExpressionContext();
break;
case DbType.Kdbndp:
expContext = new KdbndpExpressionContext();
break;
default:
throw new Exception("不支持");

2、Where条件的解析

基本和写EF一样常用的都会支持

Expression<Func<DataTestInfo2, bool>> exp = it => it.Bool2== b.Value;
expContext.Resolve(exp, ResolveExpressType.WhereSingle);
var value = expContext.Result.GetString();
var pars = expContext.Parameters;
//( [Bool2] = @Bool20 )

我们在写一个Like的例子

Expression<Func<Student, bool>> exp = it => it.Name.Contains(schoolData.Name);
ExpressionContext expContext = new ExpressionContext();
expContext.Resolve(exp, ResolveExpressType.WhereMultiple);
var value = expContext.Result.GetString();
var pars = expContext.Parameters;
//([it].[Name] like '%'+@MethodConst0+'%')

bool类型的解析是ORM解析的难点中的难点，情况多种多样

Expression<Func<DataTestInfo2, bool>> exp = it => it.Bool1&&it.Bool1;
SqlServerExpressionContext expContext = new SqlServerExpressionContext();
expContext.Resolve(exp, ResolveExpressType.WhereSingle);
var value = expContext.Result.GetString();
var pars = expContext.Parameters;
//( ( [Bool1]=1 ) AND ( [Bool1]=1 ) )

多样化的bool解释的支持

Expression<Func<Student, bool>> exp = it =>true&& it.Name != null;
ExpressionContext expContext = new ExpressionContext();
expContext.Resolve(exp, ResolveExpressType.WhereSingle);
var value = expContext.Result.GetString();
var pars = expContext.Parameters;
//(( 1 = 1 ) AND( [Name] IS NOT NULL ))

多表查询的支持，在多表查询中我们是需要加前缀的比如我们想要 it.id 而不是id

  Expression<Func<Student, bool>> exp = it => (it.Id > 1 && it.Name != name || it.Id == 1) || it.Name == WhereConst.name;
  ExpressionContext expContext = new ExpressionContext();
  expContext.Resolve(exp, ResolveExpressType.WhereMultiple);
  var value = expContext.Result.GetString();
  var pars = expContext.Parameters;
//(((( [it].[Id] > @Id0 ) AND ( [it].[Name] <> @Name1 )) OR ( [it].[Id] = @Id2 )) OR ( [it].[Name] = @Name3 ))

3、如何解析Select

支持实体类解析、查询单个字段解析、匿名对象解析

Expression<Func<DataTestInfo2, DataTestInfo2>> exp =it => new DataTestInfo2() {  Bool1=it.Bool1 , Bool2=it.Bool2 };
ExpressionContext expContext = new ExpressionContext();
expContext.IsSingle = false;
expContext.Resolve(exp, ResolveExpressType.SelectSingle);
var selectorValue = expContext.Result.GetString();
var pars = expContext.Parameters;
//[Bool1] AS [Bool1] , [Bool2] AS [Bool2]

Expression<Func<Student, School, object>> exp = (it, school) => new { Name = "a", Id = it.Id / 2, SchoolId = school.Id };
ExpressionContext expContext = new ExpressionContext();
expContext.IsSingle = false;
expContext.Resolve(exp, ResolveExpressType.SelectMultiple);
var selectorValue = expContext.Result.GetString();
// @constant0 AS [Name] , ( [it].[Id] / @Id1 ) AS [Id] , [school].[Id] AS [SchoolId]

3、字段名称的解析

例如orderby(it=>it.Name) 像这种我们就需要拿到Name

Expression<Func<Student, object>> exp = it => it.Name;
ExpressionContext expContext = GetContext();
expContext.Resolve(exp, ResolveExpressType.FieldSingle);
var selectorValue = expContext.Result.GetString();
//Name

统计单个字段

Expression<Func<Student, object>> exp = it =>SqlFunc.AggregateAvg(it.Id);
ExpressionContext expContext = GetContext();
expContext.Resolve(exp, ResolveExpressType.FieldMultiple);
var selectorValue = expContext.Result.GetString();
//AVG([it].[Id])

4、Sql函数的支持

Expression<Func<Student, bool>> exp = it => (it.Name.Contains("a")? 1:2)==1;
SqlServerExpressionContext expContext = new SqlServerExpressionContext();
expContext.Resolve(exp, ResolveExpressType.WhereSingle);
var value = expContext.Result.GetString();
var pars = expContext.Parameters;
//(( CASE  WHEN  ([Name] like '%'+@MethodConst0+'%')  THEN @MethodConst1  ELSE @MethodConst2 END ) = @Const3 )

支持的C#函数：

.ToString .Contains .Length

.ToLower .ToUpper .ToSubstring

.Equals .HasValue .Replace

.EndsWith .StartsWith .Trim

.HasValue .Value .AddDay .Date

和常用的Convert.ToInt32等等

SqlFunc.函数

SqlFunc函数下面包含了大量SQL函数

 SqlFunc.IF(st.Id > 1)
     .Return(st.Id)
     .ElseIF(st.Id == 1)
     .Return(st.SchoolId).End(st.Id) //等于Case when

5、其它功能

5.1 支持特性比如我表名和实体名不一样我们也可以实现

SqlServerExpressionContext expContext = new SqlServerExpressionContext();
expContext.MappingTables.Add(typeof(Student).Name,"OA_STUDENT")

列名也非常容易

SqlServerExpressionContext expContext = new SqlServerExpressionContext();
expContext.MappingColumns.Add("Id","ID",typeof(Student).Name)

5.2 支持子查询

Expression<Func<Test, bool>> exp = a => SqlFunc.Subqueryable<Sutdent>().Where(it => it.testId == a.id).Select(it => it.id） == 1);
var expContext = new SqlServerExpressionContext();
 expContext.Resolve(exp, ResolveExpressType.WhereSingle);
var value = expContext.Result.GetString();
var pars = expContext.Parameters;

6、自已动手创建ORM

通上面的学习你们想写出下面的语法应该相当容易了

 var oneClass = db.Queryable<Order, OrderItem, Custom>((o, i, c) => o.Id == i.OrderId&& o.CustomId == c.Id))
.Where(o=>o.id==1) 
.Where((o,i)=>i.xx==1) 
.OrderBy(o=>o.Id)
.Select((o,i,c)=> new ViewOrder
 {
          Id=SqlFunc.GetSelfAndAutoFill(o.Id),// o.*
          CustomName=c.Name   //[c].[Name] AS [CustomName]
}).ToList()

实现上面的功能总共用到Where的解析、列的解析和Select的解析

1、下面3个用到Where的解析

(o, i, c) => o.Id == i.OrderId&& o.CustomId == c.Id)
 o=>o.id==1
(o,i)=>i.xx==1

2、下面1个用到列的解析

o=>o.Id

3、下面1个用到Select的解析

(o,i,c)=> new ViewOrder
 {
          Id=SqlFunc.GetSelfAndAutoFill(o.Id),// o.*
          CustomName=c.Name   //[c].[Name] AS [CustomName]
}

源码下载：

你们的赞或者你们的 star 就是开源者的动力，开源不容易和气生财

https://gitee.com/sunkaixuan/SqlSugar

彩蛋：

下一篇文章我会介绍如何使用 SqlSugar 实现WebFirst模式开发代码，领先CodeFirst和DbFirst的设计和开发理念，也我十多年开发经验的汇总