Linq 集合操作

Linq 集合操作

演示代码

两个对象一个是Person，一个Address, AddressId是外键，

public class Person

{

public string ID { get; set; }

public string Name { get; set; }

public int Age { get; set; }

public double Salary { get; set; }

public DateTime Born { get; set; }

public int IdAddress { get; set; }

}

 

public class Address

{

public int IdAddress { get; set; }

public string Street { get; set; }

public int Num { get; set; }

public string City { get; set; }

}

测试数据如下

Person类

Address类

下面我会用7个方式实现7中集合操作

1. INNER JOIN 内链接
2. LEFT JOIN 左连接
3. RIGHT JOIN 右链接
4. FULL OUTER JOIN 所有
5. LEFT JOIN EXCLUDING INNER JOIN 左空
6. RIGHT JOIN EXCLUDING INNER JOIN 右空
7. FULL OUTER JOIN EXCLUDING INNER JOIN ？？ 学校数学没学好不知道专业术语！哈哈 INNER JOIN   最常用的方法，两表关联查询

标准Linq语法 var result = from p in Person.BuiltPersons() join a in Address.BuiltAddresses() on p.IdAddress equals a.IdAddress select new { Name = a.MyPerson.Name, Age = a.MyPerson.Age, PersonIdAddress = a.MyPerson.IdAddress, AddressIdAddress = a.MyAddress.IdAddress, Street = a.MyAddress.Street }; Lambda Expression:  var resultJoint = Person.BuiltPersons().Join( /// Source Collection Address.BuiltAddresses(), /// Inner Collection p => p.IdAddress, /// PK a => a.IdAddress, /// FK (p, a) => new { MyPerson = p, MyAddress = a }) /// Result Collection .Select(a => new { Name = a.MyPerson.Name, Age = a.MyPerson.Age, PersonIdAddress = a.MyPerson.IdAddress, AddressIdAddress = a.MyAddress.IdAddress, Street = a.MyAddress.Street }); Lambda表达式主要有5部分

1. Is the main Collection. 
2. Is the inner Collection.
3. Is the PK.
4. Is the FK.
5. Is the type for the result collection.  查询结果如下

LEFT JOIN

新增一个LeftJoin的扩展方法 public static IEnumerable<TResult> LeftJoin<TSource, TInner, TKey, TResult>(this IEnumerable<TSource> source, IEnumerable<TInner> inner, Func<TSource, TKey> pk, Func<TInner, TKey> fk, Func<TSource, TInner, TResult> result) { IEnumerable<TResult> _result = Enumerable.Empty<TResult>(); _result = from s in source join i in inner on pk(s) equals fk(i) into joinData from left in joinData.DefaultIfEmpty() select result(s, left); return _result; }  Lambda Expression:  var resultJoint = Person.BuiltPersons().LeftJoin( /// Source Collection Address.BuiltAddresses(), /// Inner Collection p => p.IdAddress, /// PK a => a.IdAddress, /// FK (p, a) => new { MyPerson = p, MyAddress = a }) /// Result Collection .Select(a => new { Name = a.MyPerson.Name, Age = a.MyPerson.Age, PersonIdAddress = a.MyPerson.IdAddress, AddressIdAddress = (a.MyAddress != null ? a.MyAddress.IdAddress : -1), Street = (a.MyAddress != null ? a.MyAddress.Street : "Null-Value") }); 注意：如果address为空Null需要做一个替换，否则会报错 查询结果如下

RIGHT JOIN 

Extension Method:  public static IEnumerable<TResult> RightJoin<TSource, TInner, TKey, TResult>(this IEnumerable<TSource> source, IEnumerable<TInner> inner, Func<TSource, TKey> pk, Func<TInner, TKey> fk, Func<TSource, TInner, TResult> result) { IEnumerable<TResult> _result = Enumerable.Empty<TResult>(); _result = from i in inner join s in source on fk(i) equals pk(s) into joinData from right in joinData.DefaultIfEmpty() select result(right, i); return _result; }  Lambda Expression:  var resultJoint = Person.BuiltPersons().RightJoin( /// Source Collection Address.BuiltAddresses(), /// Inner Collection p => p.IdAddress, /// PK a => a.IdAddress, /// FK (p, a) => new { MyPerson = p, MyAddress = a }) /// Result Collection .Select(a => new { Name = (a.MyPerson != null ? a.MyPerson.Name : "Null-Value"), Age = (a.MyPerson != null ? a.MyPerson.Age : -1), PersonIdAddress = (a.MyPerson != null ? a.MyPerson.IdAddress : -1), AddressIdAddress = a.MyAddress.IdAddress, Street = a.MyAddress.Street }); 查询结果如下

FULL OUTER JOIN 

Extension Method:  public static IEnumerable<TResult> FullOuterJoinJoin<TSource, TInner, TKey, TResult>(this IEnumerable<TSource> source, IEnumerable<TInner> inner, Func<TSource, TKey> pk, Func<TInner, TKey> fk, Func<TSource, TInner, TResult> result) { var left = source.LeftJoin(inner, pk, fk, result).ToList(); var right = source.RightJoin(inner, pk, fk, result).ToList(); return left.Union(right); }  Lambda Expression:  var resultJoint = Person.BuiltPersons().FullOuterJoinJoin( /// Source Collection Address.BuiltAddresses(), /// Inner Collection p => p.IdAddress, /// PK a => a.IdAddress, /// FK (p, a) => new { MyPerson = p, MyAddress = a }) /// Result Collection .Select(a => new { Name = (a.MyPerson != null ? a.MyPerson.Name : "Null-Value"), Age = (a.MyPerson != null ? a.MyPerson.Age : -1), PersonIdAddress = (a.MyPerson != null ? a.MyPerson.IdAddress : -1), AddressIdAddress = (a.MyAddress != null ? a.MyAddress.IdAddress : -1), Street = (a.MyAddress != null ? a.MyAddress.Street : "Null-Value") }); 注意：每个对象都需要验证Null 查询结果如下

LEFT EXCLUDING JOIN 

Extension Method:  public static IEnumerable<TResult> LeftExcludingJoin<TSource, TInner, TKey, TResult>(this IEnumerable<TSource> source, IEnumerable<TInner> inner, Func<TSource, TKey> pk, Func<TInner, TKey> fk, Func<TSource, TInner, TResult> result) { IEnumerable<TResult> _result = Enumerable.Empty<TResult>(); _result = from s in source join i in inner on pk(s) equals fk(i) into joinData from left in joinData.DefaultIfEmpty() where left == null select result(s, left); return _result; }  Lambda Expression:   var resultJoint = Person.BuiltPersons().LeftExcludingJoin( /// Source Collection Address.BuiltAddresses(), /// Inner Collection p => p.IdAddress, /// PK a => a.IdAddress, /// FK (p, a) => new { MyPerson = p, MyAddress = a }) /// Result Collection .Select(a => new { Name = a.MyPerson.Name, Age = a.MyPerson.Age, PersonIdAddress = a.MyPerson.IdAddress, AddressIdAddress = (a.MyAddress != null ? a.MyAddress.IdAddress : -1), Street = (a.MyAddress != null ? a.MyAddress.Street : "Null-Value") }); 查询结果如下

RIGHT EXCLUDING JOIN

Extension Method:   public static IEnumerable<TResult> RightExcludingJoin<TSource, TInner, TKey, TResult>(this IEnumerable<TSource> source, IEnumerable<TInner> inner, Func<TSource, TKey> pk, Func<TInner, TKey> fk, Func<TSource, TInner, TResult> result) { IEnumerable<TResult> _result = Enumerable.Empty<TResult>(); _result = from i in inner join s in source on fk(i) equals pk(s) into joinData from right in joinData.DefaultIfEmpty() where right == null select result(right, i); return _result; }  Lambda Expression:    var resultJoint = Person.BuiltPersons().RightExcludingJoin( /// Source Collection Address.BuiltAddresses(), /// Inner Collection p => p.IdAddress, /// PK a => a.IdAddress, /// FK (p, a) => new { MyPerson = p, MyAddress = a }) /// Result Collection .Select(a => new { Name = (a.MyPerson != null ? a.MyPerson.Name : "Null-Value"), Age = (a.MyPerson != null ? a.MyPerson.Age : -1), PersonIdAddress = (a.MyPerson != null ? a.MyPerson.IdAddress : -1), AddressIdAddress = a.MyAddress.IdAddress, Street = a.MyAddress.Street }); 查询结果

FULL OUTER EXCLUDING JOIN  

Extension Method:   public static IEnumerable<TResult> FulltExcludingJoin<TSource, TInner, TKey, TResult>(this IEnumerable<TSource> source, IEnumerable<TInner> inner, Func<TSource, TKey> pk, Func<TInner, TKey> fk, Func<TSource, TInner, TResult> result) { var left = source.LeftExcludingJoin(inner, pk, fk, result).ToList(); var right = source.RightExcludingJoin(inner, pk, fk, result).ToList(); return left.Union(right); }  Lambda Expression:    var resultJoint = Person.BuiltPersons().FulltExcludingJoin( /// Source Collection Address.BuiltAddresses(), /// Inner Collection p => p.IdAddress, /// PK a => a.IdAddress, /// FK (p, a) => new { MyPerson = p, MyAddress = a }) /// Result Collection .Select(a => new { Name = (a.MyPerson != null ? a.MyPerson.Name : "Null-Value"), Age = (a.MyPerson != null ? a.MyPerson.Age : -1), PersonIdAddress = (a.MyPerson != null ? a.MyPerson.IdAddress : -1), AddressIdAddress = (a.MyAddress != null ? a.MyAddress.IdAddress : -1), Street = (a.MyAddress != null ? a.MyAddress.Street : "Null-Value") }); 查询结果