对于自己写着完的代码，我特别喜欢链式（来源于jQuery的影响吧），大部分时候链式就是将返回值为void类型的对象，返回this指针，直到我遇到一个特殊情况——在父类中返回子类类型。大部分情况父类都不知道子类有什么，根本没有返回子类的需求
1 public class OldWhereV2<T>
2 {
3 protected Expression<Func<T, bool>> expression = null;
4
5 public OldWhereV2<T> Where(Expression<Func<T, bool>> memberExpression
6 {
7 return this;
8 }
9
10 public OldWhereV2<T> Or(Expression<Func<T, bool>> memberExpression
11 {
12 return this;
13 }
14
15 public OldWhereV2<T> Add(Expression<Func<T, bool>> memberExpression
16 {
17 return this;
18 }
19 }
20
21 public class OldQeuryV2<T> : OldWhereV2<T>
22 {
23
24 public OldQeuryV2<T> Select(Expression<Func<T, object>> memberExpression
25 {
26 return this;
27 }
28
29 public OldQeuryV2<T> Take(int count
30 {
31 return this;
32 }
33
34 public OldQeuryV2<T> Order(Expression<Func<T, object>> memberExpression, bool asc
35 {
36 return this;
37 }
38 }
调用的时候，如果使用链式
1 var query =new OldQeuryV2<Train>( 2 .Select(x => x.Apply_Time 3 .Select(x => x.Apply_Time 4 .Select(x => x.Approval_OrgName 5 .Where(x => x.Create_Time > DateTime.Now 6 .Add(x => x.Approval_OrgName == "" 7 .Order(x => x.Approval_OrgGID, true 8 .Order(x => x.Apply_Time, false 9 .Take(10;
.Order(x => x.Approval_OrgGID, true 这行代码会报错的。因为Where返回的是OldWhereV2<T>类型，而Order方法要求OldQeuryV2<T>类型
1 public abstract class Condition<T, M> where M : Condition<T, M>
2 {
3 protected Expression<Func<T, bool>> expression = null;
4
5 public M Where(Expression<Func<T, bool>> memberExpression
6 {
7 expression = memberExpression;
8 return (Mthis;
9 }
10
11 public M Or(Expression<Func<T, bool>> memberExpression
12 {
13 if (expression == null
14 {
15 expression = memberExpression;
16 }
17 else
18 {
19 var invokedExpr = Expression.Invoke(memberExpression, expression.Parameters.Cast<Expression>(;
20 expression = Expression.Lambda<Func<T, bool>>(Expression.OrElse(expression.Body, invokedExpr, expression.Parameters;
21 }
22 return (Mthis;
23 }
24
25 public M Add(Expression<Func<T, bool>> memberExpression
26 {
27 if (expression == null
28 {
29 expression = memberExpression;
30 }
31 else
32 {
33 var invokedExpr = Expression.Invoke(memberExpression, expression.Parameters.Cast<Expression>(;
34 expression = Expression.Lambda<Func<T, bool>>(Expression.AndAlso(expression.Body, invokedExpr, expression.Parameters;
35 }
36 return (Mthis;
37 }
38 }
39
40 public class Qeury<T> : Condition<T, Qeury<T>>
41 {
42 List<MemberInfo> selects = new List<MemberInfo>(;
43 Dictionary<MemberInfo, bool> orders = new Dictionary<MemberInfo, bool>(;
44 int count = 1000;
45
46 public Qeury<T> Select(Expression<Func<T, object>> memberExpression
47 {
48 MemberInfo memberInfo = memberExpression.GetMemberInfo(;
49 if (!selects.Contains(memberInfo
50 {
51 selects.Add(memberInfo;
52 }
53 return this;
54 }
55
56 public Qeury<T> Take(int count
57 {
58 this.count = count;
59 return this;
60 }
61
62 public Qeury<T> Order(Expression<Func<T, object>> memberExpression, bool asc
63 {
64 MemberInfo memberInfo = memberExpression.GetMemberInfo(;
65 if (orders.ContainsKey(memberInfo
66 {
67 orders[memberInfo] = asc;
68 }
69 else
70 {
71 orders.Add(memberInfo, asc;
72 }
73 return this;
74 }
75
76 public string QeurySql(
77 {
78 var queryInfo = new QueryInfo(
79 {
80 WhereExpression = this.expression,
81 SelectFields = this.selects,
82 Orders = this.orders,
83 Count = this.count
84 };
85
86 return TableAnalysis.GetTableInfo(typeof(T.QeurySql(queryInfo;
87 }
88 }
这里将Condition<T>类修改为Condition<T,M> 而M是Condition<T,M>的子类，返回的时候只需要返回M类型就好了，当然由于Condition返回了子类，所以我把它设置成了抽象类，但是也可以不用。由于Qeury<T> :实现了Condition<T, Qeury<T>>，所以子类就可以正常调用父类的方法了。
1 var query =new Qeury<Train>( 2 .Select(x => x.Apply_Time 3 .Select(x => x.Apply_Time 4 .Select(x => x.Approval_OrgName 5 .Where(x => x.Create_Time > DateTime.Now 6 .Add(x => x.Approval_OrgName == "" 7 .Order(x => x.Approval_OrgGID, true 8 .Order(x => x.Apply_Time, false 9 .Take(10;
这个算是奇技淫巧，发出来给大家看看，不过不链式不久没有烦恼了吗，正常如下面定义就好了
1 public class OldCondition<T> 2 { 3 public void Where(Expression<Func<T, bool>> memberExpression 4 { 5 6 } 7 8 public void Or(Expression<Func<T, bool>> memberExpression 9 { 10 11 } 12 13 public void Add(Expression<Func<T, bool>> memberExpression 14 { 15 16 } 17 } 18 19 public class OldQeury<T> : OldCondition<T> 20 { 21 public void Select(Expression<Func<T, object>> memberExpression 22 { 23 24 } 25 26 public void Take(int count 27 { 28 29 } 30 31 public void Order(Expression<Func<T, object>> memberExpression, bool asc 32 { 33 34 } 35 }