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
注意：本文归作者所有，未经作者允许，不得转载
