如何在LINQ中的多个where条件之间执行“或"运算 [英] How to perform 'OR' operation between several where conditions in LINQ

问题描述

我正在使用IQueryable构建查询.

I am using an IQueryable to build my query.

 IQueryable<PropertyPosts> posts = context.PropertyPosts;

之后，根据几种条件，我将 Where 子句添加到查询中，

After that based on several conditions I am appending Where clause into my query,

 if (item.ApartmentCondo == 1)
 {
    posts= posts.Where(x => x.name == item.name &&
                            x.PropertyType == PropertyType.ApartmentCondo );

 }
 if (item.House == 1)
 {
  posts= posts.Where(x => x.name == item.name &&
                            x.PropertyType == PropertyType.House );

 }

注意:还有其他一些条件.

Note: There are several other where conditions also.

之后，当我执行以下查询时，

After that when I perform the following query,

 List<PropertyPosts> posts2 = posts.ToList();

上述所有条件条件将被与".

All the above where conditions will be 'AND'ed.

但是相反，我需要对条件"条件进行或"操作.

But instead I need the Where conditions to be 'OR'ed.

这意味着我需要一种方法来附加几个Where条件，但是所有这些条件应该在它们之间执行"OR"条件.

Which means I need a way to append several Where conditions, but all these conditions should be performing 'OR' condition between them.

我该如何实现?有没有一种替代方法，而不是使用"在哪里"?

How can I achieve this? Is there an alternative way rather than using 'Where'?

推荐答案

您可以使用以下类:

/// <summary>
/// Enables the efficient, dynamic composition of query predicates.
/// </summary>
public static class PredicateBuilder
{
    /// <summary>
    /// Creates a predicate that evaluates to true.
    /// </summary>
    public static Expression<Func<T, bool>> True<T>() { return param => true; }

    /// <summary>
    /// Creates a predicate that evaluates to false.
    /// </summary>
    public static Expression<Func<T, bool>> False<T>() { return param => false; }

    /// <summary>
    /// Creates a predicate expression from the specified lambda expression.
    /// </summary>
    public static Expression<Func<T, bool>> Create<T>(Expression<Func<T, bool>> predicate) { return predicate; }

    /// <summary>
    /// Combines the first predicate with the second using the logical "and".
    /// </summary>
    public static Expression<Func<T, bool>> AND<T>(this Expression<Func<T, bool>> first, Expression<Func<T, bool>> second)
    {
        return first.Compose(second, Expression.AndAlso);
    }

    /// <summary>
    /// Combines the first predicate with the second using the logical "or".
    /// </summary>
    public static Expression<Func<T, bool>> OR<T>(this Expression<Func<T, bool>> first, Expression<Func<T, bool>> second)
    {
        return first.Compose(second, Expression.OrElse);
    }

    /// <summary>
    /// Negates the predicate.
    /// </summary>
    public static Expression<Func<T, bool>> Not<T>(this Expression<Func<T, bool>> expression)
    {
        var negated = Expression.Not(expression.Body);
        return Expression.Lambda<Func<T, bool>>(negated, expression.Parameters);
    }

    /// <summary>
    /// Combines the first expression with the second using the specified merge function.
    /// </summary>
    static Expression<T> Compose<T>(this Expression<T> first, Expression<T> second, Func<Expression, Expression, Expression> merge)
    {
        // zip parameters (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 the parameters in the first
        var secondBody = ParameterRebinder.ReplaceParameters(map, second.Body);

        // create a merged lambda expression with parameters from the first expression
        return Expression.Lambda<T>(merge(first.Body, secondBody), first.Parameters);
    }

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

        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);
        }
    }
}

您可以将其用于您的情况:

You can use it for your case:

var predicate = PredicateBuilder.False<PropertyPosts>();
//predicate = predicate.OR(x=>x.SomeProperties == someValues);
//predicate = predicate.AND(x=>x.SomeOtherProperties == someOtherValues);

if (item.ApartmentCondo == 1)
{
    predicate = predicate.OR(x => x.name == item.name &&
                        x.PropertyType == PropertyType.ApartmentCondo );
}
if (item.House == 1)
{
   predicate = predicate.OR(x => x.name == item.name &&
                        x.PropertyType == PropertyType.House );
}

List<PropertyPosts> posts2 = posts.Where(predicate).ToList();

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