问题：.net中的distinct方法对于自定义的类（class model ）去重时失效。问题分析：
model1:
1 public class TestModel1
2 {
3 public int Id { get; set; }
4 public string Name { get; set; }
5 public string Address { get; set; }
6 }
model2:
public class TestModel2
{
protected bool Equals(TestModel2 other)
{
return Id == other.Id && string.Equals(Name, other.Name) && string.Equals(Address, other.Address);
}
public override int GetHashCode()
{
unchecked
{
int hashCode = Id;
hashCode = (hashCode*397) ^ (Name != null ? Name.GetHashCode() : 0);
hashCode = (hashCode*397) ^ (Address != null ? Address.GetHashCode() : 0);
return hashCode;
}
}
public int Id { get; set; }
public string Name { get; set; }
public string Address { get; set; }
public override bool Equals(object obj)
{
if (ReferenceEquals(null, obj)) return false;
if (ReferenceEquals(this, obj)) return true;
if (obj.GetType() != this.GetType()) return false;
return Equals((TestModel2) obj);
}
}
Model3:
public class TestModel3
{
public int Id { get; set; }
public string Name { get; set; }
public string Address { get; set; }
}
public class ListTestModel3 : IEqualityComparer<TestModel3>
{
public bool Equals(TestModel3 x, TestModel3 y)
{
if (x.Id == y.Id && x.Name == y.Name && x.Address == y.Address)
{
return true;
}
return false;
}
public int GetHashCode(TestModel3 obj)
{
return 0;
}
}
主程序：
1 public partial class Form1 : Form
2 {
3 public Form1()
4 {
5 InitializeComponent();
6 InitData();
7
8 }
9
10 private void InitData()
11 {
12
13 var model1s = new List<TestModel1>();
14 var model2s = new List<TestModel2>();
15 var model3s = new List<TestModel3>();
16 for (int i = 0; i < 3; i++)
17 {
18 var model1 = new TestModel1()
19 {
20 Id = 10001,
21 Name = "张三",
22 Address = "中国-上海"
23 };
24 var model2 = new TestModel2()
25 {
26 Id = 10001,
27 Name = "张三",
28 Address = "中国-上海"
29 };
30 var model3 = new TestModel3()
31 {
32 Id = 10001,
33 Name = "张三",
34 Address = "中国-上海"
35 };
36 model1s.Add(model1);
37 model2s.Add(model2);
38 model3s.Add(model3);
39 }
40
41 for (int i = 0; i < 3; i++)
42 {
43 var model1 = new TestModel1()
44 {
45 Id = 10002,
46 Name = "张三",
47 Address = "中国-上海"
48 };
49 var model2 = new TestModel2()
50 {
51 Id = 10002,
52 Name = "张三",
53 Address = "中国-上海"
54 };
55 var model3 = new TestModel3()
56 {
57 Id = 10002,
58 Name = "张三",
59 Address = "中国-上海"
60 };
61 model1s.Add(model1);
62 model2s.Add(model2);
63 model3s.Add(model3);
64 }
65 for (int i = 0; i < 3; i++)
66 {
67 var model1 = new TestModel1()
68 {
69 Id = 10001,
70 Name = "李四",
71 Address = "中国-上海"
72 };
73 var model2 = new TestModel2()
74 {
75 Id = 10001,
76 Name = "李四",
77 Address = "中国-上海"
78 };
79 var model3 = new TestModel3()
80 {
81 Id = 10001,
82 Name = "李四",
83 Address = "中国-上海"
84 };
85 model1s.Add(model1);
86 model2s.Add(model2);
87 model3s.Add(model3);
88 }
89 for (int i = 0; i < 3; i++)
90 {
91 var model1 = new TestModel1()
92 {
93 Id = 10002,
94 Name = "李四",
95 Address = "中国-上海"
96 };
97 var model2 = new TestModel2()
98 {
99 Id = 10002,
100 Name = "李四",
101 Address = "中国-上海"
102 };
103 var model3 = new TestModel3()
104 {
105 Id = 10002,
106 Name = "李四",
107 Address = "中国-上海"
108 };
109 model1s.Add(model1);
110 model2s.Add(model2);
111 model3s.Add(model3);
112 }
113 var model4s = (from m in model1s
114 select new TestModel1
115 {
116 Id = m.Id,
117 Name = m.Name,
118 Address = m.Address
119 }).ToList().Distinct();
120 dataGridView1.DataSource = model1s;
121 dataGridView2.DataSource = model2s;
122 dataGridView3.DataSource = model3s;
123 dataGridView4.DataSource = model4s.ToList(); ;
124 }
125
126 private void InitDistinctData()
127 {
128
129 var model1s = new List<TestModel1>();
130 var model2s = new List<TestModel2>();
131 var model3s = new List<TestModel3>();
132 for (int i = 0; i < 3; i++)
133 {
134 var model1 = new TestModel1()
135 {
136 Id = 10001,
137 Name = "张三",
138 Address = "中国-上海"
139 };
140 var model2 = new TestModel2()
141 {
142 Id = 10001,
143 Name = "张三",
144 Address = "中国-上海"
145 };
146 var model3 = new TestModel3()
147 {
148 Id = 10001,
149 Name = "张三",
150 Address = "中国-上海"
151 };
152 model1s.Add(model1);
153 model2s.Add(model2);
154 model3s.Add(model3);
155 }
156
157 for (int i = 0; i < 3; i++)
158 {
159 var model1 = new TestModel1()
160 {
161 Id = 10002,
162 Name = "张三",
163 Address = "中国-上海"
164 };
165 var model2 = new TestModel2()
166 {
167 Id = 10002,
168 Name = "张三",
169 Address = "中国-上海"
170 };
171 var model3 = new TestModel3()
172 {
173 Id = 10002,
174 Name = "张三",
175 Address = "中国-上海"
176 };
177 model1s.Add(model1);
178 model2s.Add(model2);
179 model3s.Add(model3);
180 }
181 for (int i = 0; i < 3; i++)
182 {
183 var model1 = new TestModel1()
184 {
185 Id = 10001,
186 Name = "李四",
187 Address = "中国-上海"
188 };
189 var model2 = new TestModel2()
190 {
191 Id = 10001,
192 Name = "李四",
193 Address = "中国-上海"
194 };
195 var model3 = new TestModel3()
196 {
197 Id = 10001,
198 Name = "李四",
199 Address = "中国-上海"
200 };
201 model1s.Add(model1);
202 model2s.Add(model2);
203 model3s.Add(model3);
204 }
205 for (int i = 0; i < 3; i++)
206 {
207 var model1 = new TestModel1()
208 {
209 Id = 10002,
210 Name = "李四",
211 Address = "中国-上海"
212 };
213 var model2 = new TestModel2()
214 {
215 Id = 10002,
216 Name = "李四",
217 Address = "中国-上海"
218 };
219 var model3 = new TestModel3()
220 {
221 Id = 10002,
222 Name = "李四",
223 Address = "中国-上海"
224 };
225 model1s.Add(model1);
226 model2s.Add(model2);
227 model3s.Add(model3);
228 }
229 var model4s = (from m in model1s
230 select new
231 {
232 Id = m.Id,
233 Name = m.Name,
234 Address = m.Address
235 }).ToList().Distinct();
236 dataGridView1.DataSource = model1s.Distinct().ToList();
237 dataGridView2.DataSource = model2s.Distinct().ToList();
238 dataGridView3.DataSource = model3s.Distinct(new ListTestModel3()).ToList();
239 dataGridView4.DataSource = model4s.ToList();
240 }
241
242 private void button1_Click(object sender, EventArgs e)
243 {
244 InitDistinctData();
245
246 }
过滤前结果：
过滤后结果：
分析：model1不管过滤前和过滤后均没有去重，model2 重写了Equals 和GetHashCode两个方法，过滤前后结果不一样， model3实现了IEqualityComparer接口进行了Distinct时重写Equals 和GetHashCode两个方法。效果和model2是一样的。Model4，去重之前用的是自己定义的实体类，框架不知道相等的条件，顾虽然去重但是没有效果，过滤后Model4采用了匿名方法类，简单的匿名类型内部实际是键值对，框架内部使用默认的相等比较器对值进行比较，所以可以去重。
结论：自定义类无法实现多键值去重（Distinct），可以通过以上三种方法去实现。
.net Distinct 去重问题分析,布布扣,bubuko.com
时间： 2024-11-03 21:04:07