.Net Core C# - LINQ 查询运算符可以按逻辑分隔吗？

Question

假设我有六个LINQ queries。每个查询都包含上一个查询使用的运算符，并在链中再添加一个运算符：

Foo = await
(
    _context.Foo
        .Where(f => (Convert.ToDateTime(f.date1) - today).TotalDays < 31)
 )
 .ToListAsync(); 

Foo = await
(
    _context.Foo
        .Where(f => (Convert.ToDateTime(f.date1) - today).TotalDays < 31)
        .Where(f => f.recordid == x)
 )
 .ToListAsync(); 

Foo = await
(
    _context.Foo
        .Where(f => (Convert.ToDateTime(f.date1) - today).TotalDays < 31)
        .Where(f => f.recordid == x)
        .Where(f => !StatusExceptionList.Contains(r.Status))
 )
 .ToListAsync(); 

Foo = await
(
    _context.Foo
        .Where(f => (Convert.ToDateTime(f.date1) - today).TotalDays < 31)
        .Where(f => f.recordid == x)
        .Where(f => !StatusExceptionList.Contains(r.Status))
        .OrderBy(f => f.date1)
 )
 .ToListAsync(); 

Foo = await
(
    _context.Foo
        .Where(f => (Convert.ToDateTime(f.date1) - today).TotalDays < 31)
        .Where(f => f.recordid == x)
        .Where(f => !StatusExceptionList.Contains(r.Status))
        .OrderBy(f => f.date1)
        .ThenBy(f => f.date2)
)
.ToListAsync(); 

Foo = await
(
    _context.Foo
        .Where(f => (Convert.ToDateTime(f.date1) - today).TotalDays < 31)
        .Where(f => f.recordid == x)
        .Where(f => !StatusExceptionList.Contains(r.Status))
        .OrderBy(f => f.date1)
        .ThenBy(f => f.date2)
        .ThenBy(f => f.recordid)
)
.ToListAsync(); 

我想将其压缩为一个查询，并在不同的 linq 运算符之间编织逻辑，正如此伪代码所示，但这根本不起作用。我用谷歌搜索了一下，不知道下一步该尝试什么：

Foo = await
(
    _context.Foo
        .Where(f => (Convert.ToDateTime(f.date1) - today).TotalDays < 31)
        if (some logic)
        {
            .Where(f => f.recordid == x)
        }
        if (some different logic)
        {           
            .Where(f => !StatusExceptionList.Contains(r.Status))
        }
        if (some different logic)
        {
            .OrderBy(f => f.date1)
        }
        if (some different logic)
        {
            .ThenBy(f => f.date2)
        }
        if (some different logic)
        {
            .ThenBy(f => f.recordid)
        }
)
.ToListAsync(); 

谁能指出我正确的方向或告诉我我是否试图以错误的方式解决这个问题？非常感谢！！！

Answer 1

只需将查询存储在单独的变量中：

IQueryable<Foo> query = _context.Foo
    .Where(f => (Convert.ToDateTime(f.date1) - today).TotalDays < 31);

然后附加您的支票：

if (someCondition) {
    query = query.Where(f.recordid == x);
}

等等。最后 - 运行查询：

Foo = await query.ToListAsync();

使用OrderBy 和ThenBy - 检查查询是否已经是IOrderedQueryable：

if (someCondition) {
    var ordered = query as IOrderedQueryable<Foo>;
    if (ordered != null)
        query = ordered.ThenBy(x => x.field);
    else 
        query = query.OrderBy(x => x.field);
}

Answer 2

您可以构造查询，然后等待其结果：

IQueryable<Foo> query = _context.Foo
    .Where(f => (Convert.ToDateTime(f.date1) - today).TotalDays < 31);
if (some logic) {
    query = query.Where(f => f.recordid == x);
}
if (some different logic) { 
    query = query.Where(f => !StatusExceptionList.Contains(r.Status));
}
if (some ordering logic 1) {
    query = query.OrderBy(f => f.date1);
}
if (some ordering logic 2) {
    query = ((IOrderedQueryable<Foo>)query).ThenBy(f => f.date2);
}
if (some ordering logic 3) {
    query = ((IOrderedQueryable<Foo>)query).ThenBy(f => f.recordid);
}

重要的是“一些排序逻辑1”弱于“一些排序逻辑2”和“一些排序逻辑3”，否则转换不会成功。

另一种方法是创建一个Where 条件：

Foo = await
(
    _context.Foo
        .Where(f => (Convert.ToDateTime(f.date1) - today).TotalDays < 31
        && (conditionFor2 && f.recordid == x)
        && (conditionFor3 && !StatusExceptionList.Contains(r.Status))
).ToListAsync(); 

Answer 3

你可以分配一个变量：

var query = _context.Foo
    .Where(f => (Convert.ToDateTime(f.date1) - today).TotalDays < 31);

if (something)
{
    query = query.Where(f => !StatusExceptionList.Contains(r.Status));
}

等等。

最后：

var result = await query.ToListAsync();