如何为IEnumerable.Any编写Linq.Expression

Question

我正在用我的代码编写查询，这是Linq to Sql。我对表达式不是很熟悉，我想写一个表达式来检查IEnumerable中的任何一项是否满足条件

public class TestClass1
{
    // can be any number of properties, with diff names and types
    public string TestProperty1 { get; set; }
    public string TestProperty2 { get; set; }
    public List<TestClass1ExtraFieldValue> TestClass1ExtraFieldValueList { get; set; }
}

public class TestClass1ExtraFieldValue
{
    public TestClass1ExtraField TestClass1ExtraField { get; set; }

    // property names below are same in all classes which name ends with ExtraFieldValue
    public int IntValue { get; set; }
    public bool BoolValue { get; set; }
    public DateTime DateTimeValue { get; set; }
    public string StringValue { get; set; }
}

public class TestClass1ExtraField
{
    // property names are same in all classes which name ends with ExtraField
    public string Property1 { get; set; }
    public string Property2 { get; set; }
}

public class TestClass2
{
    // can be any number of properties, with diff names and types
    public string TestProperty1 { get; set; }
    public string TestProperty2 { get; set; }
    public List<TestClass2ExtraFieldValue> TestClass2ExtraFieldValueList { get; set; }
}

public class TestClass2ExtraFieldValue
{
    public TestClass2ExtraField TestClass2ExtraField { get; set; }

    // property names below are same in all classes which name ends with ExtraFieldValue
    public int IntValue { get; set; }
    public bool BoolValue { get; set; }
    public DateTime DateTimeValue { get; set; }
    public string StringValue { get; set; }
}

public class TestClass2ExtraField
{
    // property names are same in all classes  which name ends with ExtraField
    public string Property1 { get; set; }
    public string Property2 { get; set; }
}

public class TestClass3
{
    // can be any number of properties, with diff names and types
    public string TestProperty1 { get; set; }
    public string TestProperty2 { get; set; }
    public List<TestClass3ExtraFieldValue> TestClass3ExtraFieldValueList { get; set; }
}

public class TestClass3ExtraFieldValue
{
    public TestClass3ExtraField TestClass3ExtraField { get; set; }

    // property names below are same in all classes which name ends with ExtraFieldValue
    public int IntValue { get; set; }
    public bool BoolValue { get; set; }
    public DateTime DateTimeValue { get; set; }
    public string StringValue { get; set; }
}

public class TestClass3ExtraField
{
    // property names are same in all classes which name ends with ExtraField
    public string Property1 { get; set; }
    public string Property2 { get; set; }
}

// NOT a DB class
public class ExtraFieldClass
{
    public string Property1 { get; set; }
    public string Property2 { get; set; }
    public int IntValue { get; set; }
    public bool BoolValue { get; set; }
    public DateTime DateTimeValue { get; set; }
    public string StringValue { get; set; }
}

我有如下查询类：

public class TestClass1Query
{
    public string TestValue1;
    public string TestValue2;

    List<ExtraFieldClass> ExtraFieldsList { get; set; }

    public IQueryable GetQuery()
    {
        var query = GetTestClass1Values().Where(c=> c.TestProperty1==TestValue1 && c.TestProperty2 == TestValue2);
        // some condition checks
        foreach (var extraField in ExtraFieldsList)
        {
            switch (extraField.Type)
            {
                    case FieldType.Boolean:
                    {
                        var boolValue = Convert.ToBoolean(extraField.Fieldvalue);
                        query = query.Where(c => c.TestClass1ExtraFieldValueList.Any(t => t.TestClass1ExtraField.Property1 == extraField.Property1
                                                                                      && t.TestClass1ExtraField.Property2 == extraField.Property2
                                                                                      && t.BoolValue == boolValue));
                        break;
                    }

                    case FieldType.DateTime:
                    {
                        var dateTimeValue = Convert.ToDateTime(extraField.Fieldvalue);
                        query = query.Where(c => c.TestClass1ExtraFieldValueList.Any(t => t.TestClass1ExtraField.Property1 == extraField.Property1
                                                                                      && t.TestClass1ExtraField.Property2 == extraField.Property2
                                                                                      && t.DateTimeValue == dateTimeValue));
                        break;
                    }

                    case FieldType.Text:
                    {
                        var stringValue = Convert.ToString(extraField.Fieldvalue);
                        query = query.Where(c => c.TestClass1ExtraFieldValueList.Any(t => t.TestClass1ExtraField.Property1 == extraField.Property1
                                                                                      && t.TestClass1ExtraField.Property2 == extraField.Property2
                                                                                      && t.StringValue == stringValue));
                        break;
                    }

                    case FieldType.Integer:
                    {
                        var integerValue = Convert.ToInt32(extraField.Fieldvalue);
                        query = query.Where(c => c.TestClass1ExtraFieldValueList.Any(t => t.TestClass1ExtraField.Property1 == extraField.Property1
                                                                                      && t.TestClass1ExtraField.Property2 == extraField.Property2
                                                                                      && t.IntValue == integerValue));
                        break;
                    }
            }
        }
        return query;
    }

    private IQueryable<TestClass1> GetTestClass1Values()
    {
        return null;
    }
}

public class TestClass2Query
{
    public string TestValue1;
    public string TestValue2;

    List<ExtraFieldClass> ExtraFieldsList { get; set; }

    public IQueryable GetQuery()
    {
        var query = GetTestClass2Values().Where(c => c.TestProperty1 == TestValue1 && c.TestProperty2 == TestValue2);
        // some condition checks
        foreach (var extraField in ExtraFieldsList)
        {
            switch (extraField.Type)
            {
                case FieldType.Boolean:
                    {
                        var boolValue = Convert.ToBoolean(extraField.Fieldvalue);
                        query = query.Where(c => c.TestClass2ExtraFieldValueList.Any(t => t.TestClass2ExtraField.Property1 == extraField.Property1
                                                                                      && t.TestClass2ExtraField.Property2 == extraField.Property2
                                                                                      && t.BoolValue == boolValue));
                        break;
                    }

                case FieldType.DateTime:
                    {
                        var dateTimeValue = Convert.ToDateTime(extraField.Fieldvalue);
                        query = query.Where(c => c.TestClass2ExtraFieldValueList.Any(t => t.TestClass2ExtraField.Property1 == extraField.Property1
                                                                                      && t.TestClass2ExtraField.Property2 == extraField.Property2
                                                                                      && t.DateTimeValue == dateTimeValue));
                        break;
                    }

                case FieldType.Text:
                    {
                        var stringValue = Convert.ToString(extraField.Fieldvalue);
                        query = query.Where(c => c.TestClass2ExtraFieldValueList.Any(t => t.TestClass2ExtraField.Property1 == extraField.Property1
                                                                                      && t.TestClass2ExtraField.Property2 == extraField.Property2
                                                                                      && t.StringValue == stringValue));
                        break;
                    }

                case FieldType.Integer:
                    {
                        var integerValue = Convert.ToInt32(extraField.Fieldvalue);
                        query = query.Where(c => c.TestClass2ExtraFieldValueList.Any(t => t.TestClass2ExtraField.Property1 == extraField.Property1
                                                                                      && t.TestClass2ExtraField.Property2 == extraField.Property2
                                                                                      && t.IntValue == integerValue));
                        break;
                    }
            }
        }
        return query;
    }

    private IQueryable<TestClass2> GetTestClass2Values()
    {
        return null;
    }
}

public class TestClass3Query
{
    public string TestValue1;
    public string TestValue2;

    List<ExtraFieldClass> ExtraFieldsList { get; set; }

    public IQueryable GetQuery()
    {
        var query = GetTestClass3Values().Where(c => c.TestProperty1 == TestValue1 && c.TestProperty2 == TestValue2);
        // some condition checks
        foreach (var extraField in ExtraFieldsList)
        {
            switch (extraField.Type)
            {
                case FieldType.Boolean:
                    {
                        var boolValue = Convert.ToBoolean(extraField.Fieldvalue);
                        query = query.Where(c => c.TestClass3ExtraFieldValueList.Any(t => t.TestClass3ExtraField.Property1 == extraField.Property1
                                                                                      && t.TestClass3ExtraField.Property2 == extraField.Property2
                                                                                      && t.BoolValue == boolValue));
                        break;
                    }

                case FieldType.DateTime:
                    {
                        var dateTimeValue = Convert.ToDateTime(extraField.Fieldvalue);
                        query = query.Where(c => c.TestClass3ExtraFieldValueList.Any(t => t.TestClass3ExtraField.Property1 == extraField.Property1
                                                                                      && t.TestClass3ExtraField.Property2 == extraField.Property2
                                                                                      && t.DateTimeValue == dateTimeValue));
                        break;
                    }

                case FieldType.Text:
                    {
                        var stringValue = Convert.ToString(extraField.Fieldvalue);
                        query = query.Where(c => c.TestClass3ExtraFieldValueList.Any(t => t.TestClass3ExtraField.Property1 == extraField.Property1
                                                                                      && t.TestClass3ExtraField.Property2 == extraField.Property2
                                                                                      && t.StringValue == stringValue));
                        break;
                    }

                case FieldType.Integer:
                    {
                        var integerValue = Convert.ToInt32(extraField.Fieldvalue);
                        query = query.Where(c => c.TestClass3ExtraFieldValueList.Any(t => t.TestClass3ExtraField.Property1 == extraField.Property1
                                                                                      && t.TestClass3ExtraField.Property2 == extraField.Property2
                                                                                      && t.IntValue == integerValue));
                        break;
                    }
            }
        }
        return query;
    }

    private IQueryable<TestClass3> GetTestClass3Values()
    {
        return null;
    }
}

现在，如果您看到我的查询类，每个类都有自己的条件检查，并且对于额外的字段，逻辑是相同的，只是名称发生了变化。我有20个类似的班级。我不想在任何地方都有相同的重复代码。我搜索了一下，才知道我们可以使用linq-expressions来实现这一点。

我对写表达式一无所知，有什么建议或方法可以做到这一点吗？

Answer 1

您编写的Linq实际上被转换为SQL命令。在您的例子中，您已经创建了相当复杂的Match函数，它太复杂了，无法自动转换成SQL语句。

要解决这个问题，您必须从Match方法中提取switch语句并创建内联查询：

var input = new Parameter();
// ...init input
query = query.Where(a => a.Property1 == "sometext");

switch(input.Type)
{
    Case bool:
        var boolValue = Convert.ToBoolean(input.ObjectValue);
        query = query.Where(a => a.Collection.Any(b => b.TestValue.C1 == input.Parameter1 && b.TestValue.C2 == input.Parameter && b.BoolValue == boolValue);
        break;
    Case dateTime :
        // convert to datetime and check
        var dateTimeValue = Convert.ToDateTime(input.ObjectValue);
        query = query.Where(a=> a.Collection.Any(b => b.TestValue.C1 == input.Parameter1 && b.TestValue.C2 == input.Parameter && b.DateTimeValue == dateTimeValue );
        break;
    Case int:
        // convert to int and check
        // ...
        break;
}

看起来不是最好的代码，但它应该可以工作。

编辑

你可以通过将丑陋的部分移到可重用的分离函数中来改进它：

public IQueryable<ITest2> ApplyFilterOnQuery(IQueryable<ITest2> query, Parameter input)
{
    switch(input.Type)
    {
        Case bool:
            var boolValue = Convert.ToBoolean(input.ObjectValue);
            query = query.Where(a => a.Collection.Any(b => b.TestValue.C1 == input.Parameter1 && b.TestValue.C2 == input.Parameter && b.BoolValue == boolValue);
            break;
        Case dateTime :
            // convert to datetime and check
            var dateTimeValue = Convert.ToDateTime(input.ObjectValue);
            query = query.Where(a => a.Collection.Any(b => b.TestValue.C1 == input.Parameter1 && b.TestValue.C2 == input.Parameter && b.DateTimeValue == dateTimeValue );
            break;
        Case int:
            // convert to int and check
            // ...
            break;
    }
    return query;
}

然后，您可以这样使用它：

var input = new Parameter();
// ...init input
query = query.Where(a => a.Property1 == "sometext");
query = ApplyFilterOnQuery(query, input);