entityframework多条件查询类

最新推荐文章于 2022-05-26 11:03:12 发布

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最新推荐文章于 2022-05-26 11:03:12 发布

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原文链接：http://www.cnblogs.com/renzaijianghu/p/4216835.html

本文介绍使用EntityFramework进行复杂多条件查询的方法，包括构造表达式树实现逻辑判断及分页功能。通过ParameterReplacer类统一ParameterExpression，利用PredicateExtensions类实现逻辑与或运算。

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entityframework多条件查询类

var dataaccess = new BaseAccess();
            int totalCount = 0;
            var paramS = new OrderModelField[1];
            paramS[0].IsDesc = true;
            paramS[0].PropertyName = "B_Email";
            Expression<Func<Rm_Sec_UserData, bool>> expr = PredicateExtensions.True<Rm_Sec_UserData>().And(t => t.F_Email.Equals(pUserEmail)).And(t => t.F_UserPass == pPassword);

            var list = dataaccess.GetListPaged(1, 2,expr, out totalCount, paramS);

 //
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);
    }
}
/// <summary>
/// 统一ParameterExpression
/// </summary>
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;
    }
}

转载于:https://www.cnblogs.com/renzaijianghu/p/4216835.html