Hello StackOverflowers,
There is something I don't get about MyBatis resultMap.
The model I'm working on is beeing updated. We decided to create a new graph of objects which reflects our future DB schema (the current one is awful).
To sum up our problem, here is a simple case:
The current Object whith is related to table SITE is org.example.model.SiteModel. We created a new Object called org.example.entity.Site. (The package name is temporary).
The goal is now to use the existing SQL request developed thank to MyBatis and add a new ResultMap linked to the return type of our method.
Here is a an example:
/**
* Get all site defined as template.
*/
#Select("SELECT * FROM SITE WHERE ISTEMPLATE = 'True'")
#ResultMap({"siteResMap" , "siteResultMap"})
#Options(statementType = StatementType.CALLABLE)
<T> List<T> findTemplates();
Then, in an XML configuration file, we defined the following mappings:
...
<resultMap id="siteResMap" type="org.example.entity.Site" />
<resultMap id="siteResultMap" type="org.example.model.SiteModel" />
...
And then we call the method from our DAO:
List<Site> site = siteDao.findTemplates();
List<SiteModel> siteMod = siteDao.findTemplates();
What we are expecting from this is a dynamic interpretation from MyBatis, taking the right ResultMap according to the computed return type.
But both list are shown as List<org.example.entity.Site> from debuger.
It makes me think that the first ResultMap is taken, ignoring the second one.
Am I missing something ? Is there a way to make MyBatis behave in such way ?
Regards
After a lot a research and code exploration, we found out that the String[] of ResultMap is not designed to link java return types to the resultMap.
This is function retrieving the resultmap (from org.apache.ibatis.executor.resultset.DefaultResultSetHandler)
public List<Object> handleResultSets(Statement stmt) throws SQLException {
ErrorContext.instance().activity("handling results").object(mappedStatement.getId());
final List<Object> multipleResults = new ArrayList<Object>();
int resultSetCount = 0;
ResultSetWrapper rsw = getFirstResultSet(stmt);
List<ResultMap> resultMaps = mappedStatement.getResultMaps();
int resultMapCount = resultMaps.size();
validateResultMapsCount(rsw, resultMapCount);
while (rsw != null && resultMapCount > resultSetCount) {
ResultMap resultMap = resultMaps.get(resultSetCount);
handleResultSet(rsw, resultMap, multipleResults, null);
rsw = getNextResultSet(stmt);
cleanUpAfterHandlingResultSet();
resultSetCount++;
}
String[] resultSets = mappedStatement.getResulSets();
if (resultSets != null) {
while (rsw != null && resultSetCount < resultSets.length) {
ResultMapping parentMapping = nextResultMaps.get(resultSets[resultSetCount]);
if (parentMapping != null) {
String nestedResultMapId = parentMapping.getNestedResultMapId();
ResultMap resultMap = configuration.getResultMap(nestedResultMapId);
handleResultSet(rsw, resultMap, null, parentMapping);
}
rsw = getNextResultSet(stmt);
cleanUpAfterHandlingResultSet();
resultSetCount++;
}
}
return collapseSingleResultList(multipleResults);
}
It explains why we always got a List of elements of type of the first resultMap.
We created a new Dao to map new object types.
Related
I have the following child object that we use an expression to map our 'entity' to our 'domain' model. We use this when specifically calling our ChildRecordService method GetChild or GetChildren:
public static Expression<Func<global::Database.Models.ChildRecord, ChildRecord>> MapChildRecordToCommon = entity => new ChildRecord
{
DateTime = entity.DateTime,
Type = entity.Type,
};
public static async Task<List<ChildRecord>> ToCommonListAsync(this IQueryable<global::Database.Models.ChildRecord> childRecords)
{
var items = await
childRecords.Select(MapChildRecordToCommon).ToListAsync().EscapeContext();
return items;
}
public async Task<List<ChildRecord>> GetChildRecords()
{
using (var uow = this.UnitOfWorkFactory.CreateReadOnly())
{
var childRecords= await uow.GetRepository<IChildRecordRepository>().GetChildRecords().ToCommonListAsync().EscapeContext();
return childRecords;
}
}
So that all works just fine. However we have another object that is a parent to that child, that in SOME cases, we also wish to get the child during the materialisation and mapping process.
In other words the standard object looks as such:
private static Expression<Func<global::Database.Models.Plot, Plot>> MapPlotToCommonBasic = (entity) => new Plot
{
Id = entity.Id,
Direction = entity.Direction,
Utc = entity.Utc,
Velocity = entity.Velocity,
};
However what I also want to map is the Plot.ChildRecord property, using the expression MapChildRecordToCommon I have already created. I made a second expression just to test this:
private static Expression<Func<global::Database.Models.Plot, Plot>> MapPlotToCommonAdvanced = (entity) => new Plot
{
ChildRecord = MapChildRecordToCommon.Compile() (entity.ChildRecord)
};
This fails:
System.NotSupportedException
The LINQ expression node type 'Invoke' is not supported in LINQ to Entities.
Is there a way to reuse my existing expression for ChildRecord, to materialise the object of ChildRecord (ie. one to one/singular not multiple) on the Plot object? I think my trouble is caused by there being just one object and being unable to use the .Select(Map) method. I am not too great at expressions and have hit a wall with this.
For reference, there are actually up to 5 or 6 other child objects on the "Plot" object that I also want to make expressions for.
I resolved this by using the third party library LinqKit.
The library allowed the use of 2 methods, .AsExpandable() (which allows for the expressions to properly compile and be invoked as I understand), and .Invoke() as an extension method to an expression, rather than calling Expression.Invoke(yourexpression). I included a null check just in case.
My code now looks as follows:
public static async Task<List<Plot>> ToCommonListAsync(this IQueryable<global::Database.Models.Plot> plots)
{
var items = await
plots.AsExpandable().Select(MapPlotToCommon).ToListAsync().EscapeContext();
return items;
}
private static Expression<Func<global::Database.Models.Plot, Plot>> MapPlotToCommon = (entity) => new Plot
{
Id = entity.Id,
Direction = entity.Direction,
Utc = entity.Utc,
Velocity = entity.Velocity,
ChildRecord = entity.ChildRecord != null ? MapChildRecordToCommon.Invoke(entity.ChildRecord) : default
};
public static Expression<Func<global::Database.Models.ChildRecord, ChildRecord>> MapChildRecordToCommon = entity => new ChildRecord
{
DateTime = entity.DateTime,
Type = entity.Type,
};
How can I get ResultSetMetaData using MyBatis. I can't use INFORMATION_SCHEMA.columns as I have a complex dynamic query joins with multiple tables. For example, I need Number of records(this one I can get based on list size), List of Columns and data type of each column. I browsed a lot and haven't got the right ways to use it.
Please suggest the right way to get ResultSetMetaData either with TypeHandler or some other options with small example ?
I have 2 scenarios.
Scenario 1:
My Query reads a file using Abinitio QueryIt service (It consider files similar to table and can use SQL query to read). Those files are received from various up streams and not fixed set of columns. It can be N number of columns and any data type. Once my query reads the data from file, it will be sent to UI to display in Grid with formatted output based on data type (Integer, Double, String, Date) for user view. To build the Grid model, I need to know number of columns and datatype as well (for formatting). Until I know Number of Columns and Data Type of each column, I can’t build the grid model. Return type of my mapper will be List<Map<String, Object>>.
Scenario 2(for different process): Similar to above method, query reads data from multiple tables instead of reading from file based on criteria selection from UI. Here also number of columns are dynamic for grid based on selection from UI. Hence, I need number of columns and data type of each column. Return type is same as above type.
Thanks in advance.
For complicated queries, you can add custom mappers. I typically create extended mappers in separate directories so they don't get replaced when you generate again. Also, this keeps all custom SQL together.
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.company.core.app.db.mapper.custom.SomethingExtendedMapper">
<resultMap id="SomethingMap" type="com.company.core.app.db.Something">
<result column="ID" jdbcType="INTEGER" property="somethingId" />
<result column="LAST_CHANGE_DATE" jdbcType="DATE" property="lastChangeDate"
...
</resultMap>
<select id="getSomething" resultMap="SomethingMap" parameterType="Integer">
select
*
from
something
join something else...
WHERE SOMETHING_ID = #{id}
</select>
</mapper>
Then this would be the interface:
public interface SomethingExtendedMapper {
public List<Something> getSomething(#Param("id") Integer id);
}
You can write a custom TypeHanlder that extends BaseTypeHandler, which would give you access to ResultSetMetaData. I have previously written such a handler to convert a Date to a LocalDate. This is a bit of a hack to your answer because the mapper would not directly return a List<Map<String, Object>>, but that could be a property on the object that you are returning.
#MappedTypes(LocalDate.class)
public class DbLocalDateTypeHandler extends BaseTypeHandler<LocalDate> {
#Override
public void setNonNullParameter(PreparedStatement ps, int i, LocalDate parameter, JdbcType jdbcType) throws SQLException {
if (parameter == null) {
ps.setDate(i, null);
} else {
ps.setDate(i, Date.valueOf(parameter));
}
}
#Override
public LocalDate getNullableResult(ResultSet rs, String columnName) throws SQLException {
Date date = rs.getDate(columnName);
if (date != null) {
return date.toLocalDate();
}
return null;
}
#Override
public LocalDate getNullableResult(ResultSet rs, int columnIndex) throws SQLException {
Date date = rs.getDate(columnIndex);
if (date != null) {
return date.toLocalDate();
}
return null;
}
#Override
public LocalDate getNullableResult(CallableStatement cs, int columnIndex) throws SQLException {
Date date = cs.getDate(columnIndex);
if (date != null) {
return date.toLocalDate();
}
return null;
}
}
Then in your resultMap you just need to reference that handler:
<result column="CREATE_DATE" jdbcType="DATE" property="createDate" typeHandler="com.company.core.framework.db.DbLocalDateTypeHandler"/>
Lastly, if you do not need the ResultSetMetaData you could look into creating a custom ObjectFactory.
e.g.
How to return an Optional from MyBatis query
Helpful MyBatis Docs:
http://www.mybatis.org/mybatis-3/configuration.html#typeHandlers
http://www.mybatis.org/mybatis-3/configuration.html#objectFactory
I am attempting to accept from the browser a List and use this within a SQL query to a postgres database. I have the following code snippet that tries to show the function that I have made todo this. Some of the variables have been changed in case there appears to be discrepancies.
static public List<Map<String,Object>> fetch(NamedParameterJdbcTemplate jdbcTemplate, List<Integer> id){
List<Map<String,Object>> result= new ArrayList<>();
String sql = "select * from lookup where id && ARRAY[ :ids ]";
MapSqlParameterSource parameters = new MapSqlParameterSource();
parameters.addValue("ids",id, Types.INTEGER);
result= jdbcTemplate.query(sql,
parameters,
new RowMapper<Map<String,Object>>() { ...
}
)
}
The lookup tables id field is a postgress array hence me needing to use && and the array function
This function is called by many different endpoints and passes the NamedParameterJdbcTemplate as well as a list of Integers. The problem I am having is that if any integer in the list is < 100 I get the following message
Bad value for type int : {20}
Is there another way of doing this or a way around this error ?
EDIT:
It appears it was part of the problem mentioned as the answer but also using
rs.getInt(col)
instead of
rs.getArray(col)
There's an error I can see in the SQL, and probably the wrong choice of API after that. First in the query:
select * from lookup where id && ARRAY[ :ids ]
To bind an array parameter, it must not be placed in the ARRAY constructor, but rather you need to use JDBC binding like this:
select * from lookup where id && ?
As you've noticed I'm not using a named parameter in these examples, because NamedParameterJdbcTemplate does not provide a route to obtaining the java.sql.Connection object or a proxy to it. You can access it through the PreparedStatementSetter if you use the JdbcOperations interface instead.
public static List<Map<String,Object>> fetch(NamedParameterJdbcTemplate jdbcTemplate, List<Integer> idlist){
List<Map<String,Object>> result= new ArrayList<>();
String sql = "select * from lookup where id && ?";
final Integer[] ids = idlist.toArray(new Integer[0]);
PreparedStatementSetter parameters = new PreparedStatementSetter() {
#Override
void setValues(PreparedStatement stmt) {
Connection conn = stmt.getConnection();
// this can only be done through the Connection
java.sql.Array arr = conn.createArrayOf("integer", ids);
// you can use setObject(1, ids, java.sql.Types.ARRAY) instead of setArray
// in case the connection wrapper doesn't pass it on to the JDBC driver
stmt.setArray(1, ids);
}
};
JdbcOperations jdo = jdbcTemplate.getJdbcOperations();
result= jdo.query(sql,
parameters,
new RowMapper<Map<String,Object>>() { ...
}
)
}
There might be errors in the code, since I normally use a different set of APIs, and you need a try-catch block for java.sql.SQLException in that setValues function, but you should be able to handle it from here on.
I am working on a issue and i need to know that from where the
event.getData() getting the Data and which data source its using.
ddlbCompanies.addDataArrivedHandler(new DataArrivedHandler() {
#Override
public void onDataArrived(DataArrivedEvent event) {
if (event.getData() != null && !event.getData().isEmpty()){
ResultSet records = event.getData();
}
If you want to retrieve the dataSource, ResultSet has getDataSource() method.
So you can write something like: records.getDataSource().
If you want to know all the property names of the records included in the ResultSet, (assuming all records have the same properties) you can do the following:
Record rec = records.first(); //gets the first record from the ResultSet
String[] attrs = rec.getAttributes(); //get all the record attributes to a String array
The attrs array has the property names you request.
I've created an EDMX object from a database I'm programming against.
I need to get input from a user and save it to a row in the database table. The problem is that I need to limit the length of input strings to the width of the corresponding VARCHAR column in the database.
When I browse the model, I can clearly see in the properties window that the model knows the max length of the string, but I don't know how to access this data in code.
If I want to write something like this:
Entities entities = new Entities();
myTable = entities.myTable.First();
if (userInput.length > myTable.columnA.MaxLength)
{
// tell the user that the input is too long.
}
else
{
myTable.columnA = userInput;
}
How do I write it?
Update: I would like to point out that the IObjectContextAdapater mentioned in the answers below is in the System.Data.Entity.Infrastructure namespace.
Here are two methods by which you can read the meta data:
int? GetMaxLength(DbContext context, string tableName, string propertyName)
{
var oc = ((IObjectContextAdapter)context).ObjectContext;
return oc.MetadataWorkspace.GetItems(DataSpace.CSpace).OfType<EntityType>()
.Where(et => et.Name == tableName)
.SelectMany(et => et.Properties.Where(p => p.Name == propertyName))
.Select (p => p.MaxLength)
.FirstOrDefault();
}
int? GetMaxLength<T>(DbContext context, Expression<Func<T, object>> property)
{
var memberExpression = (MemberExpression)property.Body;
string propertyName = memberExpression.Member.Name;
return GetMaxLength(context, typeof(T).Name, propertyName);
}
So you can either enter the table name and property name, or an expression that specifies the property you're interested in.
Another approach could be to create a MetaData class and use the MaxLength attribute.
It's not very pretty; reading edmx properties at runtime is not something Microsoft exposed easily or documented well (or in some cases, at all). context is your DBContext.
var objectContext = ((IObjectContextAdapter)context).ObjectContext;
var entityType = objectContext.MetadataWorkspace.GetItems<EntityType>(DataSpace.CSpace).Where(e => e.Name == "your entity name").First();
var facets = entityType.Properties["your property name"].TypeUsage.Facets;
facets will look something like this, so you'll need to look for the MaxLength Name(may not exist, depending on the underlying field type) and get the Value:
Count = 5
[0]: Nullable=false
[1]: DefaultValue=null
[2]: MaxLength=250
[3]: Unicode=false
[4]: FixedLength=false
If you modify the T4 template you can add your own attribute to the properties that have MaxLength set.
If you can find the right place to add it, it's something as simple as this:
var lengthAttributeText = edmProperty.MaxLength.HasValue
? string.Format("[MaxLength({0})] ", edmProperty.MaxLength.Value)
: "";
And then add this into the text for the property line. (Tricky to be more detailed since I've already modified my .tt file a lot; also the lack of proper IDE support for .tt files makes this a lot harder than it could be.)