错误" LINQ'Indoke'的LINQ表达式类型'在Linq中不支持实体中的wery子句

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问题描述

执行查询时:

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

我获得此错误:

LINQ在Linq中不支持Linq表达节点类型'Indoke'

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;
}

我在此模式下调用该方法:

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();
}

怎么了?

推荐答案

要做您想做的事情，您需要做类似的事情:

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;
}

您可以看到，您需要进行一些表达树木管道.您以与以前相同的方式调用该方法.

现在...真的可以使用 linqkit 按 @jbl建议?是的...通过摇晃魔杖...

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;
}

注意Invoke()和Expand() linqkit方法的使用.

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问题描述

When I execute my query:

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

I obtain this error:

The LINQ expression node type 'Invoke' is not supported in LINQ to Entities

This is the method that generates the error (probably 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;
}

I invoke the method in this mode:

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();
}

What is wrong?

推荐答案

To do what you want you will need to do something like:

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;
}

As you can see you'll need to do some expression-tree plumbing. You call the method in the same way as before.

Now... is it really possible to use LinqKit as suggested by @jbl? Yes... By shaking a little the magic wand...

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;
}

Note the use of the Invoke() and Expand() LinqKit methods.

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