I would like my code to return a value but it returns me:
System.Collections.Generic.List`1[Dapper.SqlMapper+DapperRow]
I can't solve and make a right output process.
public static string Test()
{
using (IDbConnection cnn = new SQLiteConnection(LoadConnectionString()))
{
var vartest = cnn.Query("select grado from utenti where id='10'");
//var result = output.ToDictionary(row => (string)row.Grado, row => (string)row.Nome ) ; (commento)
//Console.WriteLine(vartest);
cnn.Close();
return vartest.ToString();
}
}
Query and Query<T> return multiple rows; Query is for dynamic rows; Query<T> is for typed rows. There are QueryFirst[<T>] and QuerySingle[<T>] for single rows.
If you're after a single value of a known type, then perhaps:
var vartest = cnn.QuerySingle<string>("select grado from utenti where id='10'");
if you mean your return vartest.ToString(); is returning you the string "System.Collections.Generic.List`1[Dapper.SqlMapper+DapperRow]" it is because your vartest is a list of items, you need to .ToString the item in the list
public static string ManagerFindid()
{
using (IDbConnection cnn = new SQLiteConnection(LoadConnectionString()))
{
var select = cnn.Query("select id from utenti");
if (select.Any())
{
return select[0].ToString();
// or do something with all the items in your list
foreach(string value in select)
{
//add value into list view
}
}
else
{
//this is hit when there are no items returned from the select query
return "Nothing Returned from Query";
}
}
you could also handle there being multiple items returned from your SQL
foreach(string value in select)
{
//do something with current value
}
Related
I have a c# mvc app using Dapper. There is a list table page which has several optional filters (as well as paging). A user can select (or not) any of several (about 8 right now but could grow) filters, each with a drop down for a from value and to value. So, for example, a user could select category "price" and filter from value "$100" to value "$200". However, I don't know how many categories the user is filtering on before hand and not all of the filter categories are the same type (some int, some decimal/double, some DateTime, though they all come in as string on FilterRange).
I'm trying to build a (relatively) simple yet sustainable Dapper query for this. So far I have this:
public List<PropertySale> GetSales(List<FilterRange> filterRanges, int skip = 0, int take = 0)
{
var skipTake = " order by 1 ASC OFFSET #skip ROWS";
if (take > 0)
skipTake += " FETCH NEXT #take";
var ranges = " WHERE 1 = 1 ";
for(var i = 0; i < filterRanges.Count; i++)
{
ranges += " AND #filterRanges[i].columnName BETWEEN #filterRanges[i].fromValue AND #filterRanges[i].toValue ";
}
using (var conn = OpenConnection())
{
string query = #"Select * from Sales "
+ ranges
+ skipTake;
return conn.Query<Sale>(query, new { filterRanges, skip, take }).AsList();
}
}
I Keep getting an error saying "... filterRanges cannot be used as a parameter value"
Is it possible to even do this in Dapper? All of the IEnumerable examples I see are where in _ which doesn't fit this situation. Any help is appreciated.
You can use DynamicParameters class for generic fields.
Dictionary<string, object> Filters = new Dictionary<string, object>();
Filters.Add("UserName", "admin");
Filters.Add("Email", "admin#admin.com");
var builder = new SqlBuilder();
var select = builder.AddTemplate("select * from SomeTable /**where**/");
var parameter = new DynamicParameters();
foreach (var filter in Filters)
{
parameter.Add(filter.Key, filter.Value);
builder.Where($"{filter.Key} = #{filter.Key}");
}
var searchResult = appCon.Query<ApplicationUser>(select.RawSql, parameter);
You can use a list of dynamic column values but you cannot do this also for the column name other than using string format which can cause a SQL injection.
You have to validate the column names from the list in order to be sure that they really exist before using them in a SQL query.
This is how you can use the list of filterRanges dynamically :
const string sqlTemplate = "SELECT /**select**/ FROM Sale /**where**/ /**orderby**/";
var sqlBuilder = new SqlBuilder();
var template = sqlBuilder.AddTemplate(sqlTemplate);
sqlBuilder.Select("*");
for (var i = 0; i < filterRanges.Count; i++)
{
sqlBuilder.Where($"{filterRanges[i].ColumnName} = #columnValue", new { columnValue = filterRanges[i].FromValue });
}
using (var conn = OpenConnection())
{
return conn.Query<Sale>(template.RawSql, template.Parameters).AsList();
}
You can easily create that dynamic condition using DapperQueryBuilder:
using (var conn = OpenConnection())
{
var query = conn.QueryBuilder($#"
SELECT *
FROM Sales
/**where**/
order by 1 ASC
OFFSET {skip} ROWS FETCH NEXT {take}
");
foreach (var filter in filterRanges)
query.Where($#"{filter.ColumnName:raw} BETWEEN
{filter.FromValue.Value} AND {filter.ToValue.Value}");
return conn.Query<Sale>(query, new { filterRanges, skip, take }).AsList();
}
Or without the magic word /**where**/:
using (var conn = OpenConnection())
{
var query = conn.QueryBuilder($#"
SELECT *
FROM Sales
WHERE 1=1
");
foreach (var filter in filterRanges)
query.Append($#"{filter.ColumnName:raw} BETWEEN
{filter.FromValue.Value} AND {filter.ToValue.Value}");
query.Append($"order by 1 ASC OFFSET {skip} ROWS FETCH NEXT {take}");
return conn.Query<Sale>(query, new { filterRanges, skip, take }).AsList();
}
The output is fully parametrized SQL, even though it looks like we're doing plain string concatenation.
Disclaimer: I'm one of the authors of this library
I was able to find a solution for this. The key was to convert the List to a Dictionary. I created a private method:
private Dictionary<string, object> CreateParametersDictionary(List<FilterRange> filters, int skip = 0, int take = 0)
{
var dict = new Dictionary<string, object>()
{
{ "#skip", skip },
{ "#take", take },
};
for (var i = 0; i < filters.Count; i++)
{
dict.Add($"column_{i}", filters[i].Filter.Description);
// some logic here which determines how you parse
// I used a switch, not shown here for brevity
dict.Add($"#fromVal_{i}", int.Parse(filters[i].FromValue.Value));
dict.Add($"#toVal_{i}", int.Parse(filters[i].ToValue.Value));
}
return dict;
}
Then to build my query,
var ranges = " WHERE 1 = 1 ";
for(var i = 0; i < filterRanges.Count; i++)
ranges += $" AND {filter[$"column_{i}"]} BETWEEN #fromVal_{i} AND #toVal_{i} ";
Special note: Be very careful here as the column name is not a parameter and you could open your self up to injection attacks (as #Popa noted in his answer). In my case those values come from an enum class and not from user in put so I am safe.
The rest is pretty straight forwared:
using (var conn = OpenConnection())
{
string query = #"Select * from Sales "
+ ranges
+ skipTake;
return conn.Query<Sale>(query, filter).AsList();
}
When using the C# code below to construct a DB2 SQL query the result set only has one row. If I manually construct the "IN" predicate inside the cmdTxt string using string.Join(",", ids) then all of the expected rows are returned. How can I return all of the expected rows using the db2Parameter object instead of building the query as a long string to be sent to the server?
public object[] GetResults(int[] ids)
{
var cmdTxt = "SELECT DISTINCT ID,COL2,COL3 FROM TABLE WHERE ID IN ( #ids ) ";
var db2Command = _DB2Connection.CreateCommand();
db2Command.CommandText = cmdTxt;
var db2Parameter = db2Command.CreateParameter();
db2Parameter.ArrayLength = ids.Length;
db2Parameter.DB2Type = DB2Type.DynArray;
db2Parameter.ParameterName = "#ids";
db2Parameter.Value = ids;
db2Command.Parameters.Add(db2Parameter);
var results = ExecuteQuery(db2Command);
return results.ToArray();
}
private object[] ExecuteQuery(DB2Command db2Command)
{
_DB2Connection.Open();
var resultList = new ArrayList();
var results = db2Command.ExecuteReader();
while (results.Read())
{
var values = new object[results.FieldCount];
results.GetValues(values);
resultList.Add(values);
}
results.Close();
_DB2Connection.Close();
return resultList.ToArray();
}
You cannot send in an array as a parameter. You would have to do something to build out a list of parameters, one for each of your values.
e.g.: SELECT DISTINCT ID,COL2,COL3 FROM TABLE WHERE ID IN ( #id1, #id2, ... #idN )
And then add the values to your parameter collection:
cmd.Parameters.Add("#id1", DB2Type.Integer).Value = your_val;
Additionally, there are a few things I would do to improve your code:
Use using statements around your DB2 objects. This will automatically dispose of the objects correctly when they go out of scope. If you don't do this, eventually you will run into errors. This should be done on DB2Connection, DB2Command, DB2Transaction, and DB2Reader objects especially.
I would recommend that you wrap queries in a transaction object, even for selects. With DB2 (and my experience is with z/OS mainframe, here... it might be different for AS/400), it writes one "accounting" record (basically the work that DB2 did) for each transaction. If you don't have an explicit transaction, DB2 will create one for you, and automatically commit after every statement, which adds up to a lot of backend records that could be combined.
My personal opinion would also be to create a .NET class to hold the data that you are getting back from the database. That would make it easier to work with using IntelliSense, among other things (because you would be able to auto-complete the property name, and .NET would know the type of the object). Right now, with the array of objects, if your column order or data type changes, it may be difficult to find/debug those usages throughout your code.
I've included a version of your code that I re-wrote that has some of these changes in it:
public List<ReturnClass> GetResults(int[] ids)
{
using (var conn = new DB2Connection())
{
conn.Open();
using (var trans = conn.BeginTransaction(IsolationLevel.ReadCommitted))
using (var cmd = conn.CreateCommand())
{
cmd.Transaction = trans;
var parms = new List<string>();
var idCount = 0;
foreach (var id in ids)
{
var parm = "#id" + idCount++;
parms.Add(parm);
cmd.Parameters.Add(parm, DB2Type.Integer).Value = id;
}
cmd.CommandText = "SELECT DISTINCT ID,COL2,COL3 FROM TABLE WHERE ID IN ( " + string.Join(",", parms) + " ) ";
var resultList = new List<ReturnClass>();
using (var reader = cmd.ExecuteReader())
{
while (reader.Read())
{
var values = new ReturnClass();
values.Id = (int)reader["ID"];
values.Col1 = reader["COL1"].ToString();
values.Col2 = reader["COL2"].ToString();
resultList.Add(values);
}
}
return resultList;
}
}
}
public class ReturnClass
{
public int Id;
public string Col1;
public string Col2;
}
Try changing from:
db2Parameter.DB2Type = DB2Type.DynArray;
to:
db2Parameter.DB2Type = DB2Type.Integer;
This is based on the example given here
I have a web-site connected to a SQL Server database, and I want to add a simple SQL query to it (for administrators). I was hoping to use the DataContext, and run a query, then return the results as a simple list. Is there any way to do this?
Using
string full_query = "SELECT " + query;
IEnumerable<string> results = DB.DB().ExecuteQuery<string>(full_query);
Doesn't work, throwing errors where ints come through. Changing the template parameter to "object" doesn't help much either.
So I need to run a select statement, and return the results as a list on a page.
Any ideas?
Normally you would want to use:
var results = DB.DB().SqlQuery(full_query);
If you want insert/update/delete, you can use:
DB.DB().ExecuteSqlCommand(full_query);
Hope it helps.
After a bit of messing around, I found something that works. I am using a class called DatabaseResults to hold the results:
public class DatabaseResults
{
public List<string> ColumnNames { get; set; }
public List<List<string>> Rows { get; set; }
public DatabaseResults()
{
ColumnNames = new List<string>();
Rows = new List<List<string>>();
}
}
The method then goes and runs the query, grabbing the headings and putting them in the results objects. It then reads the rows, taking the strings of the column values. "query" is the string passed in. It is the "select" query, with the select bit missing.
DatabaseResults results = new DatabaseResults();
string full_query = "SELECT " + query;
DbConnection connection = DB.DB().Connection;
connection.Open();
var command = connection.CreateCommand();
command.CommandText = full_query;
try
{
using (var reader = command.ExecuteReader())
{
for (int i = 0; i < reader.FieldCount; i++)
{
results.ColumnNames.Add(reader.GetName(i));
}
while (reader.Read())
{
List<string> this_res = new List<string>();
for (int i = 0; i < reader.FieldCount; ++i)
{
this_res.Add(reader[i].ToString());
}
results.Rows.Add(this_res);
}
}
}
catch (Exception ex)
{
results.ColumnNames.Add("Error");
List<string> this_error = new List<string>();
this_error.Add(ex.Message);
results.Rows.Add(this_error);
}
finally
{
connection.Close();
}
I can't destroy the connection, as it is used by the systems db object, so I need to open and close it. The try/catch/finally makes sure this happens.
private void GetRecDept()
{
cmbDept.Items.Clear();
ListViewMeasurements.Items.Clear();
SFCDataContext SFC = new SFCDataContext();
try
{
var query = (from i in SFC.Systems_SettingsMeasurements
orderby i.RowID descending
select new {
RowID = i.RowID,
Measure = i.Measurement,
Target = i.TargetPercentage,
Dept = i.Department_ID
});
foreach (var w in query)
{
ListViewItem List = new ListViewItem(w.RowID.ToString());
List.SubItems.Add(w.Measure);
List.SubItems.Add(string.Format("{0:n2}", w.Target));
List.SubItems.Add(w.Dept);
ListViewMeasurements.Items.AddRange(new ListViewItem[] { List });
}
foreach (var r in query)
{
cmbDept.Items.Add(r.Dept.Distinct());
}
}
catch (Exception ex)
{
MessageBox.Show(ex.Message.ToString());
}
}
Its output on the cmbDept.Items.Add() is showing this kind of string
System.Linq.Enumerable+<DistinctIterator>d__7a1[System.Char]` unlike
in the listview how can i convert it to a string type readable to
users it's in a combo box.
Try this:
var distinctDept = query.Select(x=>x.Dept).Distinct().ToArray();
cmbDept.Items.AddRange(distinctDept)
About your issue, the Dept is string, when you use cmbDept.Items.Add(r.Dept.Distinct()); the added item is an IEnumerable<char> and of course it can't display that as you expected, the ToString() is called before displaying the IEnumerable<char> and gives you the result as you described.
I have created an asp.net application using Entity Framework. In this I want to add the records into a list. For this I have to use the foreach loop but it always adding only last record data for all records, meaning it's showing same data. Here I have pasted my code. Please verify it once and guide where I can change.
public List<CategoryItems> ListMenuCategory(int MenuId)
{
string str = string.Empty;
string strJSON = string.Empty;
List<CategoryItems> resultmenu;
resultmenu = new List<CategoryItems>();
List<CategoryItems> Result;
Result = new List<CategoryItems>();
bool check = true;
var objmenuCategory = from cat in objEntity.menucategories where cat.MenuId == MenuId && cat.Active == check select cat;
CategoryItems Categorylist = new CategoryItems();
foreach (menucategory category in objmenuCategory)
{
Categorylist.CategoryName = category.CategoryName;
Categorylist.Description = category.Description;
int menuid = category.MenuCategoryId;
List<menuitem> menuitems = GetMenucategories(menuid);
foreach (var items in menuitems)
{
Categorylist.ItemName = items.ItemName;
Categorylist.Description = items.Description;
Categorylist.Price = (float)items.Price;
string Image = items.Picture;
Categorylist.Picture = "http://restaurantmanager.testshell.net/Images/" + Image;
Categorylist.Thumbnail = "http://restaurantmanager.testshell.net/Images/" + items.Thumbnail;
if (items.CreatedDate != null)
{
Categorylist.CreatedDate = (DateTime)items.CreatedDate;
}
if (items.ModifiedDate != null)
{
Categorylist.ModifiedDate = (DateTime)items.ModifiedDate;
}
Result.Add(Categorylist);
}
// Result.AddRange(menus);
}
return Result;
}
private List<menuitem> GetMenucategories(int p)
{
restaurantEntities objEntity1 = new restaurantEntities();
var menuitems = from items in objEntity1.menuitems where items.MenuCategoryId == p select items;
return menuitems.ToList();
}
You are creating the Categorylist item outside of the loops, so you are only using one single item, filling it with different data and adding it over and over to the result.
You have to create the item inside the innermost loop, so that each iteration gets its own object.
Note: ChrisF also spotted that you call AddRange inside the loop, which has the result that you will add the same set of items over and over. You don't need to call AddRange at all, you can just skip the Result list entirely and just return resultmenu instead.