c# - 带有参数的 LINQ“位置”

Question

我确定这是菜鸟的错误，但我自己找不到答案。

public class Database : DataContext 
{
    public Table<Record> RecordTable;
    public Database(string connection) : base(connection) {}
}

[Table(Name = "RecordsTable")]
public class Record
{
    [Column( IsPrimaryKey = true, CanBeNull = false)]
    public int codedID;
}

// inside some class
private void ReadTestData(Database openedDatabase, int expectedValue)
{
    Table<Record> rec = openedDatabase.GetTable<Record>();
    var q =
        from a in rec
        where (GetMonth == expectedValue)   // <--- that line doesn't work
        select a;

    foreach (var b in q) { System.Console.WriteLine("something"); }
}

static Expression<Func<Record, int>> GetMonth = a => a.codedID/10000;

public static int DecodeMonth(int codedID)
{
    int month = codedID/10000;
    //(...)
    return month;
}

我想调用DecodeMonth函数并将其返回值与预期值进行比较。我该怎么做？

我做了一些研究并设法运行这样的代码：

var q = openedDatabase.RecordTable.Where(GetMonthBool);

static Expression<Func<Record, bool>> GetMonthBool = a => (a.codedID/10000 == 1);

但是expectedValue 被硬编码为“1”——这并不能解决我的问题。

Answer 1

创建一个创建这样的表达式的方法

private Expression<Func<Record, bool>> GetMonthBoolFunc(int value)
{
    return a => (a.codedID/10000 == value); 
}

var q = openedDatabase.RecordTable.Where(GetMonthBoolFunc(1));