没有获取特定表的列

Question

我正在尝试获取特定 table 的架构，但我得到的列为空。

我试图在下面得到结果 class:

public class Tables
    {
        public string Name { get; set; }
        public string[] Columns { get; set; }
    }

代码：

string[] selectedTables = { "Table1", "Table2"};
  var conectionString = new SqlConnection("MyconnectionString");
  var data = new List<Tables>();
  data = conectionString.GetSchema("Tables").AsEnumerable()
       .Select
       (
        t => new Tables
         {
           Name =  t[2].ToString(),
           Columns = conn.GetSchema("Columns",
                     new string[] { databaseName,t[2].ToString() }).AsEnumerable() // t[2].ToString() represent tablename
                    .Where(c => selectedTables.Contains(t[2].ToString()))
                    .Select(c => c[3].ToString()).ToArray()  // c[3].ToString() represent Columns
       }).ToList();

 return data;

虽然在数据中我得到了 tables 的列表，即 Table0,Table1,Table2,Table3 等，但我没有得到这个 Table1 and Table2 选择的 tables 的列。

更新：我正在寻找这样的东西：

 // You can specify the Catalog, Schema, Table Name, Table Type to get 
         // the specified table(s).
         // You can use four restrictions for Table, so you should create a 4 members array.
         String[] tableRestrictions = new String[4];

         // For the array, 0-member represents Catalog; 1-member represents Schema; 
         // 2-member represents Table Name; 3-member represents Table Type. 
         // Now we specify the Table Name of the table what we want to get schema information.
         tableRestrictions[2] = "Course";

         DataTable courseTableSchemaTable = conn.GetSchema("Tables", tableRestrictions);

data = conectionString.GetSchema("Tables").AsEnumerable()
       .Select
       (
        t => new Tables
         {
           Name =  t[2].ToString(),
            Columns = (from useTable in selectedTables
            let columns = conn.GetSchema("Columns",new string[] { databaseName, t["TABLE_SCHEMA"].ToString(), useTable })
                     select new { columns[3]})  //Error
       }).ToList();

如何注入 selectedTables？

Answer 1

有几种方法可以实现目标。

一种方法是获取所有 table，按 table 名称过滤结果，然后获取每个选定的列 table:

string[] selectedTables = { "Table1", "Table2"};
using (var conection = new SqlConnection("MyconnectionString"))
{
    connection.Open();

    var tables = (
        from table in connection.GetSchema("Tables").AsEnumerable()
        let name = (string)table["TABLE_NAME"]
        where selectedTables.Contains(name)
        let catalog = (string)table["TABLE_CATALOG"]
        let schema = (string)table["TABLE_SCHEMA"]
        select new Tables // this should really be called Table
        {
            Name = name,
            Columns = (
                from column in connection.GetSchema("Columns", new [] { catalog, schema, name }).AsEnumerable()
                select (string)column["COLUMN_NAME"]).ToArray()
        }).ToList();

    return tables;
}

更新： 根据评论，您实际上想要所有 table，但只为所选列填充列，而不是 where您可以对条件列 population 使用相同的条件：

        from table in connection.GetSchema("Tables").AsEnumerable()
        let name = (string)table["TABLE_NAME"]
        let catalog = (string)table["TABLE_CATALOG"]
        let schema = (string)table["TABLE_SCHEMA"]
        select new Tables // this should really be called Table
        {
            Name = name,
            Columns = selectedTables.Contains(name) ? (
                from column in connection.GetSchema("Columns", new [] { catalog, schema, name }).AsEnumerable()
                select (string)column["COLUMN_NAME"]).ToArray() : null
        }).ToList();

没有获取特定表的列

Not getting columns for specific tables

c#

linq

datatable

ado.net