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解析类似，有些增强。
操作元数据一般使用以下几个步骤：
- 读取EDM模型
- 获取实体结构
- 获取功能结构
- 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:
使用以下方法，可以访问XML模型中<!-- SSDL content -->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: }
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以上为使用元数据方式查询EF框架的信息属性等。