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Lambda表达式树解析（下）

2024-09-22 10:45:23   213人阅读

概述

　　前面章节，总结了Lambda树的构建，那么怎么解析Lambda表达式树那？Lambda表达式是一种委托构造而成，如果能够清晰的解析Lambda表达式树，那么就能够理解Lambda表达式要传递的正式意图。解析Lambda表达式树意义很大，比如我们用的EF框架、Rafy框架，里面封装了大量的Lambda查询表达式，通过解析表达式转换成SQL语句，即可以查询数据库，将数据呈现给前台用户；

Lambda表达式树解析

　　下面代码块是标识Express各个节点的信息，ExpressionType.Call标识表达式中含有方法调用，常用到该类型的3个参数为:Method.DeclaringType和Argument和object。ExpressionType.Quote标识表达式中含有一元表达式，常用到的参数是Operand,里面放置了Lamble具体表达式。

public string AnalysisExpression(Expression exp)        {            string TextSql = "";            switch (exp.NodeType)            {                case ExpressionType.Call:                    {                        MethodCallExpression mce = exp as MethodCallExpression;                        Console.WriteLine("The Method Is {0}", mce.Method.Name);                        Console.WriteLine("The Method TypeOf {0}", mce.Method.DeclaringType);                        if (mce.Method.DeclaringType == typeof(string))                        {                            break;                        }                        if (mce.Method.DeclaringType != typeof(Queryable)){                            break;                        }                        for (int i = 0; i < mce.Arguments.Count; i++)                        {                            TextSql+=AnalysisExpression(mce.Arguments[i]);                        }                    }                    break;                case ExpressionType.Quote:                    {                        UnaryExpression ue = exp as UnaryExpression;                        TextSql += AnalysisExpression(ue.Operand);                    }                    break;                case ExpressionType.Lambda:                    {                        LambdaExpression le = exp as LambdaExpression;                        AnalysisExpression(le.Body);                        TextSql+= ExpressTreeAnalysis.GetSqlByExpression(le.Body);                    }                    break;                case ExpressionType.AndAlso:                case ExpressionType.OrElse:                case ExpressionType.Equal:                    {                        BinaryExpression be = exp as BinaryExpression;                        Console.WriteLine("The Method Is {0}", exp.NodeType.ToString());                        TextSql += AnalysisExpression(be.Left);                        TextSql += AnalysisExpression(be.Right);                    }                    break;                case ExpressionType.Constant:                    {                        ConstantExpression ce = exp as ConstantExpression;                        Console.WriteLine("The Value Type Is {0}", ce.Value.ToString());                    }                    break;                case ExpressionType.Parameter:                    {                        ParameterExpression pe = exp as ParameterExpression;                        Console.WriteLine("The Parameter Is {0}", pe.Name);                    }                    break;                default:                    {                        Console.Write("UnKnow");                    }                    break;            }            return TextSql;        }

由于自定义集合实现IQueryable和IQueryProvider来自定义查询项

实现IQuable定义的类：

public class BlogQueryable<T> : IQueryable<T>    {        BlogQueryProvider provider;        Expression expression;        public BlogQueryable(BlogQueryProvider provider)        {            if (provider == null)            {                throw new ArgumentNullException("provider");            }            this.provider = provider;            this.expression = Expression.Constant(this);        }        public BlogQueryable(BlogQueryProvider provider, Expression expression)        {            this.provider = provider;            this.expression = expression;        }        public Type ElementType        {            get            {                return typeof(T);            }        }        public Expression Expression        {            get            {                return expression;            }        }        public IQueryProvider Provider        {            get            {                return provider;            }        }        public IEnumerator<T> GetEnumerator()        {            return ((IEnumerable<T>)this.provider.Execute(this.expression)).GetEnumerator();        }        IEnumerator IEnumerable.GetEnumerator()        {            return ((IEnumerable)this.provider.Execute(this.expression)).GetEnumerator();        }        public void Where2(Expression<Func<T, bool>> func)        {            string TextSql = ExpressTreeAnalysis.GetSqlByExpression(func.Body);        }    }

实现IQueryProvider接口的类，CreateQuery解析表达式树而Execute则是执行解析后的SQL语句，查询数据，填充list集合：

public class BlogQueryProvider : IQueryProvider
{        public IQueryable CreateQuery(Expression expression)        {            Type elementType = expression.Type;            try            {                return (IQueryable)Activator.CreateInstance(typeof(BlogQueryable<>).MakeGenericType(elementType), new object[] { this, expression });            }            catch(TargetInvocationException tie)            {                throw tie.InnerException;            }        }        public IQueryable<TElement> CreateQuery<TElement>(Expression expression)        {                       //string TextSql=  ExpressTreeAnalysis.GetSqlByExpression(((Expression)(expression as MethodCallExpression).Arguments[1]).bo);            //Console.WriteLine(TextSql);            AnalysisExpression(expression);            return new BlogQueryable<TElement>(this, expression);        }        public object Execute(Expression expression)        {            return this.Execute2<object>(expression);        }        public TResult Execute<TResult>(Expression expression)        {            return (TResult)this.Execute2<TResult>(expression);        }        public TResult Execute2<TResult>(Expression expression)        {            return (TResult)Activator.CreateInstance(typeof(TResult));        }    }

具体下面即可使用查询

        public void MyTestMethod()        {            Catagory cag = new Catagory("四大名著点评");            IList<Blog> Blogs = new List<Blog>();            Blog bok = new Blog() { Title = "红楼梦", Conent = "红楼梦书籍不错",
　　　　　　　　 User = new Author() { UserName = "曹雪芹", BirefInfor = "中国清代著名作家" } };            bok.Catagories.Add(cag);            bok.Catagories.Add(new Catagory("红楼梦专栏"));            Blogs.Add(bok);            Blog bok2 = new Blog() { Title = "三国演义", Conent = "三国鼎立时期的描述",
　　　　　　　 User = new Author() { UserName = "罗贯中", BirefInfor = "中国元末明初著名作家" } };            bok2.Catagories.Add(cag);            bok2.Catagories.Add(new Catagory("三国演义专栏"));            Blogs.Add(bok2);            Blog bok3 = new Blog() { Title = "西游记", Conent = "西游记讲述四个徒弟和一个师傅取经事情", 
              User = new Author() { UserName = "吴承恩", BirefInfor = "中国明代杰出的小说家" } };            bok2.Catagories.Add(cag);            bok2.Catagories.Add(new Catagory("西游记专栏"));            Blogs.Add(bok3);            Blog bok4 = new Blog() { Title = "水浒传", Conent = "描述梁山好汉劫富济贫的故事", 
　　　　　　　　　　User = new Author() { UserName = "施耐庵", BirefInfor = "中国明代杰出的小说家" } };            bok2.Catagories.Add(cag);            bok2.Catagories.Add(new Catagory("水浒传专栏"));            Blogs.Add(bok4);                                   BlogQueryProvider Provider = new BlogQueryProvider();            BlogQueryable<Blog> Quble = new BlogQueryable<Blog>(Provider);                                               var t2 = Quble.Where(p => p.Title == "123" &&  p.Conent.Contains("水浒"));        }

参考代码下载

后续：针对解析Lambda表达式树成SQL，本人也是刚刚入门，至于完全要解析成SQL，还需要研究......

Lambda表达式树解析（下）


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