I have a JSON value stored in SQL Server. I want to retrieve that JSON value and bind it to C# property (which is deserialized to desired entity). I want to know what would be the best practice to do that effectively? Right now, I'm doing like this:
Public class Employee
{
public int Id;
public string Name;
public int Age;
}
Public class EmployeeData
{
public string JsonEmployeeText {get;set;} // Binding the json string from database
public List<Employee> Employees { get { return JsonConvert.DeserializeObject<Employee>(JsonEmployeeText );}} //Converting the retrieved json string from Database to c# entity
}
I guess we should not do any sort of database logic on getters as it can sometimes delay the process of initialization in case we need to use this we need to make sure we enable the lazy loading
Related
Imagine we have a number of related objects (equivalently DB tables), for example:
public class Person {
private String name;
private Date birthday;
private int height;
private Job job;
private House house;
..
}
public class Job {
private String company;
private int salary;
..
}
public class House {
private Address address;
private int age;
private int numRooms;
..
}
public class Address {
private String town;
private String street;
..
}
How to best design a system for easily defining and accessing widely varying subsets of data on these objects/tables? Design patterns, pros and cons, are very welcome. I'm using Java, but this is a more general problem.
For example, I want to easily say:
I'd like some object with (Person.name, Person.height, Job.company, Address.street)
I'd like some object with (Job.company, House.numRooms, Address.town)
Etc.
Other assumptions:
We can assume that we're always getting a known structure of objects on the input, e.g. a Person with its Job, House, and Address.
The resulting object doesn't necessarily need to know the names of the fields it was constructed from, i.e. for subset defined as (Person.name, Person.height, Job.company, Address.street) it can be the array of Objects {"Joe Doe", 180, "ACompany Inc.", "Main Street"}.
The object/table hierarchy is complex, so there are hundreds of data fields.
There may be hundreds of subsets that need to be defined.
A minority of fields to obtain may be computed from actual fields, e.g. I may want to get a person's age, computed as (now().getYear() - Person.birtday.getYear()).
Here are some options I see:
A SQL view for each subset.
Minuses:
They will be almost the same for similar subsets. This is OK just for field names, but not great for the joins part, which could ideally be refactored out to a common place.
Less testable than a solution in code.
Using a DTO assembler, e.g. http://www.genericdtoassembler.org/
This could be used to flatten the complex structure of input objects into a single DTO.
Minuses:
I'm not sure how I'd then proceed to easily define subsets of fields on this DTO. Perhaps if I could somehow set the ones irrelevant to the current subset to null? Not sure how.
Not sure if I can do computed fields easily in this way.
A custom mapper I came up with.
Relevant code:
// The enum has a value for each field in the Person objects hierarchy
// that we may be interested in.
public enum DataField {
PERSON_NAME(new PersonNameExtractor()),
..
PERSON_AGE(new PersonAgeExtractor()),
..
COMPANY(new CompanyExtractor()),
..
}
// This is the container for field-value pairs from a given instance of
// the object hierarchy.
public class Vector {
private Map<DataField, Object> fields;
..
}
// Extractors know how to get the value for a given DataField
// from the object hierarchy. There's one extractor per each field.
public interface Extractor<T> {
public T extract(Person person);
}
public class PersonNameExtractor implements Extractor<String> {
public String extract(Person person) {
return person.getName();
}
}
public class PersonAgeExtractor implements Extractor<Integer> {
public int extract(Person person) {
return now().getYear() - person.getBirthday().getYear();
}
}
public class CompanyExtractor implements Extractor<String> {
public String extract(Person person) {
return person.getJob().getCompany();
}
}
// Building the Vector using all the fields from the DataField enum
// and the extractors.
public class FullVectorBuilder {
public Vector buildVector(Person person) {
Vector vector = new Vector();
for (DataField field : DataField.values()) {
vector.addField(field, field.getExtractor().extract(person));
}
return vector;
}
}
// Definition of a subset of fields on the Vector.
public interface Selector {
public List<DataField> getFields();
}
public class SampleSubsetSelector implements Selector {
private List<DataField> fields = ImmutableList.of(PERSON_NAME, COMPANY);
...
}
// Finally, a builder for the subset Vector, choosing only
// fields pointed to by the selector.
public class SubsetVectorBuilder {
public Vector buildSubsetVector(Vector fullVector, Selector selector) {
Vector subsetVector = new Vector();
for (DataField field : selector.getFields()) {
subsetVector.addField(field, fullVector.getValue(field));
}
return subsetVector;
}
}
Minuses:
Need to create a tiny Extractor class for each of hundreds of data fields.
This is a custom solution that I came up with, seems to work and I like it, but I feel this problem must have been encountered and solved before, likely in a better way.. Has it?
Edit
Each object knows how to turn itself into a Map of fields, keyed on an enum of all fields.
E.g.
public enum DataField {
PERSON_NAME,
..
PERSON_AGE,
..
COMPANY,
..
}
public class Person {
private String name;
private Date birthday;
private int height;
private Job job;
private House house;
..
public Map<DataField, Object> toMap() {
return ImmutableMap
.add(DataField.PERSON_NAME, name)
.add(DataField.BIRTHDAY, birthday)
.add(DataField.HEIGHT, height)
.add(DataField.AGE, now().getYear() - birthday.getYear())
.build();
}
}
Then, I could build a Vector combining all the Maps, and select subsets from it like in 3.
Minuses:
Enum name clashes, e.g. if Job has an Address and House has an Address, then I want to be able to specify a subset taking street name of both. But how do I then define the toMap() method in the Address class?
No obvious place to put code doing computed fields requiring data from more than one object, e.g. physical distance from Address of House to Address of Company.
Many thanks!
Over in-memory object mapping in the application, I would favor database processing of the data for better performance. Views, or more elaborate OLAP/datawarehouse tooling could do the trick. If the calculated fields remain basic, as in "age = now - birth", I see nothing wrong with having that logic in the DB.
On the code side, given the large number of DTOs you have to deal with, you could use classless dynamic (available in some JVM languages) or JSON objects. The idea is that when a data structure changes, you only need to modify the DB and the UI, saving you the cost of changing a whole bunch of classes in between.
I have several stored procedures that don't return the domain objects (i.e; objects which have corresponding sql table mapping in hbm files); but return the custom objects instead.
I want to call these stored procedures using NHibernate and fill my custom objects with the output automatically, instead of filling them mannually as I would do if I use a SqlDataReader.
An example shall be highly appreciated.
BTW: I use nhibernate 3.2 new feature mapping by code.
Maybe you can try the following (taken from https://stackoverflow.com/a/10513319/1236044 )
It uses CreateSQLQuery. You may try replacing the select... with Exec MyStoredProc
The key point is having your select or stored procedure return columns with the same name as the properties of the DTO you are trying to populate.
public class YourDto
{
public int YourDtoId { get; set; }
public string YourDtoTitle { get; set; }
}
then
var result = yourNhSession
.CreateSQLQuery("select yourColumn1 as YourDtoId, yourColumn2 as YourDtoTitle from YOUR_TABLE")
.SetResultTransformer(Transformers.AliasToBean<YourDto>())
.List<YourDto>();
Is there any way to address/refer to a SQL SERVER table, by its Unique Index rather its TableName ?
my Application is using multiple html tables, which are acutally within a form,
for CRUD opporations,(more R/U than Create or delete) of an Existing SQL Table.
now... that i need to mix two separated tables, in same update-form (that's my first 'mix')
as i am using Jquery to pass parameters to C# code behind, so it will take care of the
update opporations, and will be able to differentiate the source of the update post/request
and i do know, i could address the table by its TableName,
i just wanted to make sure, as i was searching for some information on the web,
i've encountred results with the Terms sql server 2005... table index or id,
though all results seem to have something to do with, what i can call, some kind of "manipulation", in oreder to create some indexing system /schema (i think it's like hdds has a FAT table)
and I Emphasize "Create",cause I was actualy looking for an existing /built in, numeric value for a "TableID", just the same as a Table has rows and each row has its row IDENTITY - Column.
so at this point i am turning back to the real question at the top .
so that's what i came up with aventually : a simple struct + a class to hold values for database
public class DBMetaDetails
{
public struct DbTable
{
public DbTable(string tableName, int tableId): this()
{
this.Name = tableName;
this.ID = tableId;
}
public string HtmlOutput;
public string Name { get; private set; }
public int ID { get; private set; }
}
}
public sealed class tblsIDs
{
public const int firstTbl= 1, SecondTbl = 2;
}
another class should be for table names
public sealed class tblsNames
{
public const string firstTbl= "firstTbl", SecondTbl = "SecondTbl";
}
another that will hold tables columns names ...etc
Im trying to write an aplication with uses hibernate to write to database, however in some actions i have to use JDBC on data in tables made by HB.
JDBS is requred to give administrator ability to create SQL queries with will return statistic info about data in database like number of processed document of specified type, numbers of success/failed log in attempts or total value of products in orders.
To do that i've done an from that allows to create class that has override toString() with return nice sql query string.
All works but now im trying to make administrator live easier by hiving him an ability to choose of table/column names. And here is an problem, because they are created by hibernate. some by #column annotation other by field name.
How can i check how field mapping?
I know its all about reflections but didnt do much of that in java yet.
example
#Entity
#Table(name= "my_table_name" )
public class TableOFSomething implements Serializable{
//This field isn't mapped into database and info about it is not requred.
//In fact, info about it may cause an error.
private static final long serialVersionUID = 7L;
#Id
#Column(name="id")
private String id;
private String fieldOne;
#Column(name="field_two")
private String fieldTwo;
#Column(name="renamed_just_for_fun")
private int Number;
//code with getters & setters
}
How to write methods that will have definition like
public <T> String tableName(Class<T> Target); //returns name of table in database
public <T> ArrayList<String> tabelFields(Class<T> Target); //returns name of fields in database
Hibernate has API - getClassMetadata that can explore the mapping. The API might change and is now located in another place , but i will use it and not in reflection for this.
look on this post for more details:
Get the table name from the model in Hibernate
if you want reflection , so use this link
import java.lang.reflect.Field;
import java.lang.reflect.Modifier;
import java.util.ArrayList;
import javax.persistence.Column;
import javax.persistence.Table;
import odi.beans.statistic.QueryBean;
public class ReflectionTest {
public static void main(String[] args) {
ReflectionTest test=new ReflectionTest();
System.out.println("Table name of "+QueryBean.class.getName()+" is "+test.getTableName(QueryBean.class));
System.out.println("Column names in this table are:");
for(String n: test.getColumnNames(QueryBean.class)){
System.out.println("\t"+n);
}
System.out.println("Good bye ;)");
}
public <T> ArrayList<String> getColumnNames(Class<T> target) {
ArrayList<String> ret=new ArrayList<>();
Field[] fields = target.getDeclaredFields();
String fieldName =null;
for (Field f : fields) {
//jump to next if if field is static
if (Modifier.isStatic(f.getModifiers()))
continue;
if (f.isAnnotationPresent(Column.class)) {
Column a = f.getAnnotation(Column.class);
fieldName = a.name();
} else {
fieldName = f.getName();
}
ret.add(fieldName);
}
return ret;
}
public <T> String getTableName(Class<T> target){
String ret=target.getSimpleName();
if (target.isAnnotationPresent(Table.class))
{
Table t=target.getAnnotation(Table.class);
ret=t.name();
}
return ret;
}
}
Is it cover all possibilities?
I know now that Hibernate way would be easier, but this is also about learning of very useful reflection mechanism :)
EDIT:
Important question:
Will this work only on annotations or also on xml mapping?
Hi all I have a horrid database I gotta work with and linq to sql is the option im taking to retrieve data from. anywho im trying to reuse a function by throwing in a different table name based on a user selection and there is no way to my knowledge to modify the TEntity or Table<> in a DataContext Query.
This is my current code.
public void GetRecordsByTableName(string table_name){
string sql = "Select * from " + table_name;
var records = dataContext.ExecuteQuery</*Suppossed Table Name*/>(sql);
ViewData["recordsByTableName"] = records.ToList();
}
I want to populate my ViewData with Enumerable records.
You can call the ExecuteQuery method on the DataContext instance. You will want to call the overload that takes a Type instance, outlined here:
http://msdn.microsoft.com/en-us/library/bb534292.aspx
Assuming that you have a type that is attributed correctly for the table, passing that Type instance for that type and the SQL will give you what you want.
As casperOne already answered, you can use ExecuteQuery method first overload (the one that asks for a Type parameter). Since i had a similar issue and you asked an example, here is one:
public IEnumerable<YourType> RetrieveData(string tableName, string name)
{
string sql = string.Format("Select * FROM {0} where Name = '{1}'", tableName, name);
var result = YourDataContext.ExecuteQuery(typeof(YourType), sql);
return result;
}
Pay attention to YourType since you will have to define a type that has a constructor (it can't be abstract or interface). I'd suggest you create a custom type that has exactly the same attributes that your SQL Table. If you do that, the ExecuteQuery method will automatically 'inject' the values from your table to your custom type. Like that:
//This is a hypothetical table mapped from LINQ DBML
[global::System.Data.Linq.Mapping.TableAttribute(Name="dbo.ClientData")]
public partial class ClientData : INotifyPropertyChanging, INotifyPropertyChanged
{
private int _ID;
private string _NAME;
private string _AGE;
}
//This would be your custom type that emulates your ClientData table
public class ClientDataCustomType
{
private int _ID;
private string _NAME;
private string _AGE;
}
So, on the former example, the ExecuteQuery method would be:
var result = YourDataContext.ExecuteQuery(typeof(ClientDataCustomType), sql);