C# y使用IQueryable。我没有使用EF，也无法理解如何再次使用谓词生成器。我的表TblFamilies位于LINQ pad中，可以正常运行。你能不能用PredicateBuilder构造一个可以成功运行的语句。对于PredicateBuilder，我是

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y使用

IQueryable

。我没有使用EF，也无法理解如何再次使用谓词生成器。我的表TblFamilies位于LINQ pad中，可以正常运行。你能不能用PredicateBuilder构造一个可以成功运行的语句。对于PredicateBuilder，我是否需要添加任何程序集或任何不是dotnet附带的类。是的，请访问我发布的网站，你可以在文章中获取源代码。它只是一个只有几行代码的类。我认为没有任何限制会困扰您。我在LINQPad中添加了linqkit，并尝试执行一个查询，但出现了错误

“LINQPad.User.TypedDataContext.TblFamilies”是一个“属性”，但与“type”一样使用。

上面的代码只是一个示例，不准确。在

PredicateBuilder.True

中，您应该将

TblFamile

更改为其实际的“类型”。我假设您正在使用某种ORM，比如EntityFramework之类的。如果没有，请在源

IEnumerable

实例之后调用

.AsQueryable（）

。PredicateBuilder仅适用于

IQueryable

。我没有使用EF，也无法理解如何再次使用PredicateBuilder。我的表TBLFFamilies位于LINQ pad中，可以正常运行。u plzz能否使用PredicateBuilder构造将成功运行的语句。

var sName="";

var r = from t in TblFamilies
where 1 == 1
if(sName!="")
{
  && t.Name="Keith";
};

select new
{
    t.ID,
    t.ParentID,
    t.Name,
    t.CurDate
};

r.Dump();               

var r = from t in TblFamilie
select new
{
    t.ID,
    t.ParentID,
    t.Name,
    t.CurDate
};

   if (sName!="")
        r = r.Where(x => x.Name == sName);

// begin with true if you start with And operator.
var predicate = PredicateBuilder.True<TblFamilie>();
predicate = predicate.And(t => t.CureDate < DateTime.UtcNow.AddDays(-1));
// you can mix with Or operator too.
predicate = predicate.Or(t => t.Name.Contains("blah"));

var results = context.TblFamilie
.Where(predicate)
.Select(new
{
  // your projection here...
});


// begin with false if you start with Or operator.
var predicate2 = PredicateBuilder.False<TblFamilie>();
predicate2 = predicate2.Or(t => t.CureDate < DateTime.UtcNow.AddDays(-1));
// you can mix with And operator too.
predicate2 = predicate2.And(t => t.Name.Contains("blah"));

var results = context.TblFamilie
.Where(predicate)
.Select(new
{
  // your projection here...
});


// even nesting is possible
var inner = PredicateBuilder.False<TblFamilie>();
inner = inner.Or (p => p.Name.Contains("foo"));
inner = inner.Or (p => p.Name.Contains("bar"));

var outer = PredicateBuilder.True<TblFamilie>();
outer = outer.And (p => p.CureDate > DateTime.UtcNow.AddDays(-3));
outer = outer.And (p => p.CureDate < DateTime.UtcNow.AddDays(-1));
outer = outer.And (inner);

var results = context.TblFamilie
.Where(outer)
.Select(new
{
  // your projection here...
});

// you have 4 families from DB, API or anywhere.
var failies = new List<Family>
{
    new Family { Id = 1, ParentId = 1, Name = "foo", Birthday = new DateTime(1971, 1, 1) },
    new Family { Id = 1, ParentId = 1, Name = "bar", Birthday = new DateTime(1982, 1, 1) },
    new Family { Id = 1, ParentId = 1, Name = "foobar", Birthday = new DateTime(1993, 1, 1) },
    new Family { Id = 1, ParentId = 1, Name = "fake", Birthday = new DateTime(2000, 1, 1) },
};

// make predicate!
// if a family's Birthday is before than 1980 'or' Name contains "ke".
var predicate = PredicateBuilder.True<Family>();
predicate = predicate.And(o => o.Birthday < new DateTime(1980, 1, 1));
predicate = predicate.Or(o => o.Name.Contains("ke"));

// you should make IQueryable in order to use PredicateBuilder.
var result = failies.AsQueryable()
    .Where(predicate)
    .Select(o => new
    {
        o.Id, o.Name, o.Birthday    // only project what you want.
    })
    .ToList();

// now, result should contains "foo" and "fake".
foreach (var family in result)
{
    Debug.WriteLine("Name: " + family.Name);
}

// you have 4 strings from DB, API or anywhere.
var strings = new List<string>
{
    "foo",
    "bar",
    "foobar",
    "fake"
};


// make predicate!
// if a string contains "oo" or "ke"
var predicate = PredicateBuilder.True<string>();
predicate = predicate.And(o => o.Contains("oo"));
predicate = predicate.Or(o => o.Contains("ke"));

// you should make IQueryable in order to use PredicateBuilder.
var result = strings.AsQueryable()
    .Where(predicate)
    .ToList();

// now, result should contains "foo", "foobar" and "fake".
foreach (var stringResult in result)
{
    Debug.WriteLine("Name: " + stringResult);
}