Question

我正在构建一个详细的搜索，我正在试图弄清楚如何将我的Linq查询编写到我的实体。

基本上我有用户可以在列表控件中选择1 *项。我无法理解的部分如下：

如何动态构建 Where AND（字段等于此OR字段等于此OR ...）子句物品数量不同的地方。

数据库域字段示例内容：'26,21,22,100,164,130'

示例 :(我们的想法是能够根据所选项目的数量生成此内容）

Offre.Where(o=> o.Domain.Contains("26") || o.Domain.Contains("100") )

Offre.Where(o=> o.Domain.Contains("26") )

Offre.Where(o=> o.Domain.Contains("26") || o.Domain.Contains("100") || o.Domain.Contains("22") )

然后我可以轻松地将生成的查询作为IQueryable，并添加到此对象以构建我的查询。

有人能指出我的AND（OR .. OR）条款正确的方向吗？

Answer 1

To work around this restriction, you can manually construct an expression (Source)

<强> C＃

static Expression<Func<TElement, bool>> BuildContainsExpression<TElement, TValue>(

    Expression<Func<TElement, TValue>> valueSelector, IEnumerable<TValue> values)

{

    if (null == valueSelector) { throw new ArgumentNullException("valueSelector"); }

    if (null == values) { throw new ArgumentNullException("values"); }

    ParameterExpression p = valueSelector.Parameters.Single();

    // p => valueSelector(p) == values[0] || valueSelector(p) == ...

    if (!values.Any())

    {

        return e => false;

    }

    var equals = values.Select(value => (Expression)Expression.Equal(valueSelector.Body, Expression.Constant(value, typeof(TValue))));

    var body = equals.Aggregate<Expression>((accumulate, equal) => Expression.Or(accumulate, equal));

    return Expression.Lambda<Func<TElement, bool>>(body, p);

}

使用此实用程序方法，

var query2 = context.Entities.Where(BuildContainsExpression<Entity, int>(e => e.ID, ids));

<强> VB.Net

Public Shared Function BuildContainsExpression(Of TElement, TValue)( _
ByVal valueSelector As Expression(Of Func(Of TElement, TValue)), _
ByVal values As IEnumerable(Of TValue) _
   ) As Expression(Of Func(Of TElement, Boolean))

    ' validate arguments
    If IsNothing(valueSelector) Then Throw New ArgumentNullException("valueSelector")
    If IsNothing(values) Then Throw New ArgumentNullException("values")

    Dim p As ParameterExpression = valueSelector.Parameters.Single()
    If Not values.Any Then
        Return _
            Function(e) False
    End If

    Dim equals = values.Select( _
        Function(v) _
            Expression.Equal(valueSelector.Body, Expression.Constant(v, GetType(TValue))) _
    )

    Dim body = equals.Aggregate( _
        Function(accumulate, equal) _
            Expression.Or(accumulate, equal) _
    )

    Return Expression.Lambda(Of Func(Of TElement, Boolean))(body, p)
End Function

使用此实用程序方法

   Dim query = m_data. Offer

   If (selectedSectors.Count > 0) Then
        query = query.Where(BuildContainsExpression(Function(o As Offer) o.Value, selectedSectors))
   End If

Answer 2

我认为这是你的答案：

LINQ to entities - Building where clauses to test collections within a many to many relationship

Answer 3

如果你的Offre有某种与之相关的唯一ID，你可以尝试以下方法：

List<int> queryCriteria = new List<int>;

//Fill your query criteria here

//Instead of o.Domain.Id you can use whatever ID you have.
var resultSet = Offre.Where(o => queryCriteria.Contains(o.Domain.Id));

从多个参数组成Linq to Entity Query

3 个答案: