ADO.NET实体框架Entity Framework模型-基于元数据解析

蔚落 2021-11-16 08:22 221阅读 0赞

上一篇简单介绍了EF的XML模型结构，在基于xml解析一文中，主要使用xml查询技术Xpath，XQuery来得到实体模型中相应信息的，由于这种方式在数据库庞大，表关系复杂的情况下，有诸多弊端，所有使用基于元数据解析EF将更加简单便捷，适用性强。

> 本文主要介绍EDM元数据及其操作，实现功能与[ADO.NET实体框架Entity Framework模型-基于XML解析][ADO.NET_Entity Framework_-_XML]类似，有些增强。
> 
> 操作元数据一般使用以下几个步骤：
> 
> 1.  读取EDM模型
> 2.  获取实体结构
> 3.  获取功能结构
> 4.  组织需要数据
> 
> 通过API访问EDM主要通过下面三个类：
> 
> ObjectContext，EntityConnection和MetadataWorkspace。
> 
> 在我的程序中主要使用左右一个MeadataWorkspace，该类的功能是暴露API以访问元数的。
> 
> DEM结果与元数据类的对应关系:
> 
> [![image][]][image 1]

使用以下方法，可以访问XML模型中下EntityType节点下的所有元数据。

var items=ctx.MetadataWorkspace.GetItems<EntityType>(DataSpace.CSpace);

在上篇文章中，对xmlhelper类更新为如下代码：

1:  using System;

2:  using System.Collections.Generic;

3:  using System.Linq;

4:  using System.Text;

5:  using System.Xml;

6:  using System.Collections;

7:  //using EF_XML_TableRelation;

8:  using System.Data.Metadata.Edm;

9:  using MvcApplication3.Models;

10:

11:  namespace EF_XML_TableRelation.XML

12:  {

13:      public class XmlHelper

14:      {

15:          /// <summary>

16:          /// 获取所有表的主键

17:          /// </summary>

18:          /// <returns>key：表名 value：主键</returns>

19:          public static SortedList<string, string> GetTableKEY()

20:          {

21:              SortedList<string, string> list = new SortedList<string, string>();

22:              using (testEntities context = new testEntities())

23:              {

24:                  var entities = context.MetadataWorkspace.GetItems<EntityType>(DataSpace.CSpace);

25:                  foreach (var item in entities)

26:                  {

27:                      foreach (var prop in item.Members)

28:                      {

29:                          var entityItem = item as EntityType;

30:                          if (entityItem.KeyMembers.Any(p => p.Name == prop.Name))

31:                          {

32:                              list.Add(item.Name, prop.Name);

33:                          }

34:                      }

35:                  }

36:              }

37:              return list;

38:          }

39:          /// <summary>

40:          /// 获取表的关系

41:          /// </summary>

42:          /// <param name="tablename"></param>

43:          /// <param name="IsRelation"></param>

44:          /// <returns></returns>

45:          public static List<TableRelation> GetTable(string tablename, bool IsRelation)

46:          {

47:              List<TableRelation> list = new List<TableRelation>();

48:              using (testEntities context = new testEntities())

49:              {

50:                  var entities = context.MetadataWorkspace.GetItems<EntityType>(DataSpace.CSpace);

51:                  EntityType entityItem = null;

52:                  if (IsRelation)

53:                  {

54:                      foreach (var item in entities)

55:                      {

56:                          if (entityItem == null)

57:                          {

58:                              entityItem = item as EntityType;

59:                          }

60:                          if (entityItem.NavigationProperties.Contains(item.Name) || item.Name.Equals(tablename))

61:                              list.Add(WriteProperties(item, context, DataSpace.CSpace));

62:                      }

63:                  }

64:                  else

65:                  {

66:                      foreach (var item in entities)

67:                      {

68:                          if (entityItem == null)

69:                          {

70:                              entityItem = item as EntityType;

71:                          }

72:                          if (item.Name.Equals(tablename))

73:                              list.Add(WriteProperties(item, context, DataSpace.CSpace));

74:                      }

75:                  }

76:              }

77:              return list;

78:          }

79:          /// <summary>

80:          /// 表的关系合集

81:          /// </summary>

82:          /// <param name="item"></param>

83:          /// <param name="ctx"></param>

84:          /// <param name="space"></param>

85:          /// <returns></returns>

86:          public static TableRelation WriteProperties(StructuralType item, testEntities ctx, DataSpace space)

87:          {

88:              TableRelation tr = new TableRelation();

89:              var node = (space == DataSpace.CSpace) ? "Properties" : "Columns";

90:              List<Column> list = new List<Column>();

91:

92:              foreach (var prop in item.Members)

93:              {

94:                  var entityItem = item as EntityType;

95:                  Column column = new Column();

96:

97:                  if (entityItem != null && entityItem.Properties.Contains(prop))

98:                  {

99:                      column.columnname = prop.Name;

100:                      column.title = prop.Documentation != null ? prop.Documentation.Summary : null;

101:                      column.type = prop.TypeUsage.EdmType != null ? prop.TypeUsage.EdmType.Name : null;

102:                      column.maxlength = prop.TypeUsage.Facets.Contains("MaxLength") ? prop.TypeUsage.Facets["MaxLength"].Value.ToString() : null;

103:                      if (ctx.MetadataWorkspace

104:                        .GetItems<AssociationType>(space)

105:                          .Where(a => a.IsForeignKey).Any(a =>

106:                            a.ReferentialConstraints[0]

107:                             .ToProperties[0].Name == prop.Name &&

108:                            a.ReferentialConstraints[0].ToRole.Name.Contains(item.Name)))

109:                      {

110:                          for (int i = 0; i < Realation(item, ctx, DataSpace.CSpace).Count; i++)

111:                          {

112:                              if (Realation(item, ctx, DataSpace.CSpace).Values[i].Values[0].Equals(prop.Name) &&

113:                                 Realation(item, ctx, DataSpace.CSpace).Values[i].Values[2].Contains(item.Name))

114:                              {

115:

116:                                  column.mainrole = Realation(item, ctx, DataSpace.CSpace).Values[i].Values[6].ToString();

117:                                  column.mainmultiplicity = Realation(item, ctx, DataSpace.CSpace).Values[i].Values[5].ToString();

118:                                  column.mainkey = Realation(item, ctx, DataSpace.CSpace).Values[i].Values[4].ToString();

119:                                  column.relationname = Realation(item, ctx, DataSpace.CSpace).Values[i].Values[3].ToString();

120:

121:                              }

122:

123:                          }

124:                      }

125:                      list.Add(column);

126:                  }

127:                  tr.tablename = item.Name;

128:                  tr.tabletitle = item.Documentation != null ? item.Documentation.Summary : item.Name;

129:                  tr.columns = list;

130:              }

131:              return tr;

132:          }

133:          /// <summary>

134:          /// 返回所有主表的关系

135:          /// </summary>

136:          /// <param name="item"></param>

137:          /// <param name="ctx"></param>

138:          /// <param name="space"></param>

139:          /// <returns></returns>

140:          public static SortedList<string, SortedList<string, string>> Realation(StructuralType item, testEntities ctx, DataSpace space)

141:          {

142:              SortedList<string, SortedList<string, string>> list1 = new SortedList<string, SortedList<string, string>>();

143:              var entity = ctx.MetadataWorkspace.GetItems<AssociationType>(space);

144:              foreach (var a in entity)

145:              {

146:                  var entityItem = item as EntityType;

147:                  for (int i = 0; i < entityItem.NavigationProperties.Count; i++)

148:                  {

149:                      if (entityItem.NavigationProperties[i].RelationshipType.Name.Equals(a.Name))

150:                      {

151:                          SortedList<string, string> list = new SortedList<string, string>();

152:                          list.Add("mainrole", a.ReferentialConstraints[0].ToRole.Name);

153:                          list.Add("mainkey", a.ReferentialConstraints[0].ToProperties[0].Name);

154:                          list.Add("mainmultiplicity", a.ReferentialConstraints[0].ToRole.RelationshipMultiplicity.ToString());

155:                          list.Add("subrole", a.ReferentialConstraints[0].FromRole.Name);

156:                          list.Add("subkey", a.ReferentialConstraints[0].FromProperties[0].Name);

157:                          list.Add("submultiplicity", a.ReferentialConstraints[0].FromRole.RelationshipMultiplicity.ToString());

158:                          list.Add("relationname", a.Name);

159:                          if (!list1.ContainsKey(a.Name))

160:                          {

161:                              list1.Add(a.Name, list);

162:                          }

163:                      }

164:                  }

165:              }

166:              return list1;

167:          }

168:      }

169:  }

以上为使用元数据方式查询EF框架的信息属性等。

转载于:https://www.cnblogs.com/jiangxin/p/3190603.html

[ADO.NET_Entity Framework_-_XML]: http://www.cnblogs.com/jiangxin/p/3185997.html
[image]: /images/20211116/9c17c83b5f364ba9997b42076cf7d406.png
[image 1]: http://images.cnblogs.com/cnblogs_com/qouoww/201204/201204291702226057.png