Question

当我执行查询时：

rs.Select(x => x.id).ToArray();

我收到此错误：

LINQ to Entities中不支持LINQ表达式节点类型“Invoke”

这是生成错误的方法（可能 func（x））：

public IQueryable<TEntity> Compare<TEntity>(IQueryable<TEntity> source, Func<TEntity, int> func)
{
     IQueryable<TEntity> res = source;

     if (!this.LBoundIsNull) res = res.Where(x => func(x) >= _lBound);
     if (!this.UBoundIsNull) res = res.Where(x => func(x) <= _uBound);

     return res;
}

我在这种模式下调用方法：

Document doc = new Document();
doc.Number = new RangeValues(lBound, null);

using (MyEntities db = new MyEntities())
{
    var rs = db.documents;
    if (doc.Number != null) rs = doc.Numero.Compare(rs, x => x.number);

    long[] id = rs.Select(x => x.id).ToArray();
}

有什么问题？

Answer 1

要做你想做的事，你需要做类似的事情：

public static IQueryable<TEntity> Compare<TEntity>(IQueryable<TEntity> source, Expression<Func<TEntity, int>> func)
{
    IQueryable<TEntity> res = source;

    if (!LBoundIsNull) 
    {
        Expression ge = Expression.GreaterThanOrEqual(func.Body, Expression.Constant(_lBound));
        var lambda = Expression.Lambda<Func<TEntity, bool>>(ge, func.Parameters);
        res = res.Where(lambda);
    }

    if (!UBoundIsNull)
    {
        Expression le = Expression.LessThanOrEqual(func.Body, Expression.Constant(_uBound));
        var lambda = Expression.Lambda<Func<TEntity, bool>>(le, func.Parameters);
        res = res.Where(lambda);
    }

    return res;
}

你可以看到你需要做一些表达树管道。您可以像以前一样调用该方法。

现在......是否真的可以按照@jbl的建议使用LinqKit？是的......通过摇动一点魔杖......

using LinqKit;

public static IQueryable<TEntity> Compare<TEntity>(IQueryable<TEntity> source, Expression<Func<TEntity, int>> func)
{
    IQueryable<TEntity> res = source;

    if (!LBoundIsNull)
    {
        Expression<Func<TEntity, bool>> lambda = x => func.Invoke(x) >= _lBound;
        res = res.Where(lambda.Expand());
    }

    if (!UBoundIsNull)
    {
        Expression<Func<TEntity, bool>> lambda = x => func.Invoke(x) <= _uBound;
        res = res.Where(lambda.Expand());
    }

    return res;
}

请注意使用Invoke()和Expand() LinqKit方法。

错误＆＃34; LINQ表达式节点类型＆＃39;调用＆＃39; LINQ to Entities＆＃34;不支持在方法内的where子句中

1 个答案: