using System;
using System.Collections.Generic;
using System.Linq;
using System.Linq.Expressions;
using System.Text;
using System.Threading.Tasks;
namespace Jusoft.ThirdParty.Extensions
{
internal class ParameterReplacer : ExpressionVisitor
{
public ParameterReplacer(ParameterExpression paramExpr)
{
this.ParameterExpression = paramExpr;
}
public ParameterExpression ParameterExpression { get; private set; }
public Expression Replace(Expression expr)
{
return this.Visit(expr);
}
protected override Expression VisitParameter(ParameterExpression p)
{
return this.ParameterExpression;
}
}
/// <summary>
/// Linq方法重写
/// </summary>
public static class PredicateExtensions
{
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<Func<T, bool>> And<T>(this Expression<Func<T, bool>> exp_left, Expression<Func<T, bool>> exp_right)
{
var candidateExpr = Expression.Parameter(typeof(T), "candidate");
var parameterReplacer = new ParameterReplacer(candidateExpr);
var left = parameterReplacer.Replace(exp_left.Body);
var right = parameterReplacer.Replace(exp_right.Body);
var body = Expression.And(left, right);
return Expression.Lambda<Func<T, bool>>(body, candidateExpr);
}
public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> exp_left, Expression<Func<T, bool>> exp_right)
{
var candidateExpr = Expression.Parameter(typeof(T), "candidate");
var parameterReplacer = new ParameterReplacer(candidateExpr);
var left = parameterReplacer.Replace(exp_left.Body);
var right = parameterReplacer.Replace(exp_right.Body);
var body = Expression.Or(left, right);
return Expression.Lambda<Func<T, bool>>(body, candidateExpr);
}
}
}
使用方法
Expression<Func<Customer, bool>> where = PredicateExtensions.True<CustomerList>();
if (condition.StartTime.HasValue)//时间
{
where = where.And(p => p.CreateTime > condition.StartTime && p.CreateTime <= condition.EndTime);
}
if (condition.CustomerType.HasValue)
{
where = where.And(p => p.StateId == condition.CustomerType);
}
var data = dbContext.CustomerList.Where(where);
