如何执行'OR'LINQ中几个where条件之间的操作

本文关键字：where 几个 条件 操作 之间 OR 何执行 执行 LINQ | 更新日期: 2023-09-27 18:16:58

我使用IQueryable来构建我的查询。

 IQueryable<PropertyPosts> posts = context.PropertyPosts;

之后，基于几个条件，我将Where子句附加到我的查询中，

 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:还有几个其他的条件。

之后，当我执行以下查询时，

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

上述所有中条件将被'与'处理。

但是我需要Where条件被'OR'处理。

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

我怎样才能做到这一点?是否有替代方法而不是使用'Where'?

如何执行'OR'LINQ中几个where条件之间的操作

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);
        }
    }
}

你可以把它用在你的例子中:

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();

将您的if条件移动到Where:

posts = posts.Where(x => x.name == item.name && 
                   (    (item.ApartmentCondo == 1 && x.PropertyType == PropertyType.ApartmentCondo)
                     || (item.House == 1          && x.PropertyType == PropertyType.House) );

试试这个

posts= posts.Where(x => x.name == item.name &&
                   (
                    (item.ApartmentCondo == 1 && x.PropertyType == PropertyType.ApartmentCondo) || 
                    (item.House == 1 && x.PropertyType == PropertyType.House))
                   );

对不起，我有一个新的答案，但我太少的代表评论。

True/False工作，但有点混乱，也产生多个起点。我已经修改了代码并删除了True<和False>方法，并为Create创建了一个新的重载方法。

public static class PredicateBuilder
{
    public const bool TreatEntireExpressionAsAnd = true;
    public const bool TreatEntireExpressionAsOr = false;
    public static Expression<Func<T, bool>> Create<T>(bool value = TreatEntireExpressionAsAnd) { return param => value; }
    ...
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