EF 拉姆达 动态拼接查询语句

Posted 2020-08-22 虫虫飞520

EF 动态拼接查询语句

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Linq.Expressions;
using System.Security.Cryptography;
using System.Text;

namespace Aliexpress.Common.CommonHelper
{
//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);
// }
//}

 


public class ParameterRebinder : ExpressionVisitor
{
private readonly Dictionary<ParameterExpression, ParameterExpression> map;

public ParameterRebinder(Dictionary<ParameterExpression, ParameterExpression> map)
{
this.map = map ?? new Dictionary<ParameterExpression, ParameterExpression>();
}

public static Expression ReplaceParameters(Dictionary<ParameterExpression, ParameterExpression> map, Expression exp)
{
return new ParameterRebinder(map).Visit(exp);
}

protected override Expression VisitParameter(ParameterExpression p)
{
ParameterExpression replacement;
if (map.TryGetValue(p, out replacement))
{
p = replacement;
}
return base.VisitParameter(p);
}
}

 

 


public static class PredicateBuilder
{

public static Expression<Func<T, bool>> True<T>() { return f => true; }
public static Expression<Func<T, bool>> False<T>() { return f => false; }
public static Expression<T> Compose<T>(this Expression<T> first, Expression<T> second, Func<Expression, Expression, Expression> merge)
{
// build parameter map (from parameters of second to parameters of first)
var map = first.Parameters.Select((f, i) => new { f, s = second.Parameters[i] }).ToDictionary(p => p.s, p => p.f);

// replace parameters in the second lambda expression with parameters from the first
var secondBody = ParameterRebinder.ReplaceParameters(map, second.Body);

// apply composition of lambda expression bodies to parameters from the first expression 
return Expression.Lambda<T>(merge(first.Body, secondBody), first.Parameters);
}

public static Expression<Func<T, bool>> And<T>(this Expression<Func<T, bool>> first, Expression<Func<T, bool>> second)
{
return first.Compose(second, Expression.And);
}

public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> first, Expression<Func<T, bool>> second)
{
return first.Compose(second, Expression.Or);
}
}
}