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jvx:client:model:databook:master_detail [2018/02/01 08:20] admin |
jvx:client:model:databook:master_detail [2020/06/08 15:30] (current) cduncan Edited for English grammar (capitalization, punctuation, correct verb conjugation) |
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| - | ~~Title: Using master/detail relationships~~ | + | ~~Title: Using Master/Detail Relationships~~ |
| Master/detail relationships are used to create relationships between tables or other datasets. The master can also be viewed as a group, whereas the detail contains the individual sets of the group. | Master/detail relationships are used to create relationships between tables or other datasets. The master can also be viewed as a group, whereas the detail contains the individual sets of the group. | ||
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| == Example == | == Example == | ||
| - | Our application handles the administration of countries, states and districts. Tables in the database are created in 3rd NF. The following is an excerpt from the HSQLDB: | + | Our application handles the administration of countries, states, and districts. Tables in the database are created in 3rd NF. The following is an excerpt from the HSQLDB: |
| <file sql createdb.sql> | <file sql createdb.sql> | ||
| Line 37: | Line 37: | ||
| </file> | </file> | ||
| - | As the table definition shows, countries consist of individual states and states are made up of districts. In our application we want to create a form that allows the editing of countries, states and districts, as well as the relationships between them. | + | As the table definition shows, countries consist of individual states, and states are made up of districts. In our application, we want to create a form that allows the editing of countries, states and districts, as well as the relationships between them. |
| We first create our server objects: | We first create our server objects: | ||
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| The master/detail relationship between countries and states is created via the foreign key (STATES.CTRY_ID) to the primary key (COUNTRIES.ID). This means that when a country is selected, all associated states are displayed. States that are not assigned to the selected “master” country are not shown. | The master/detail relationship between countries and states is created via the foreign key (STATES.CTRY_ID) to the primary key (COUNTRIES.ID). This means that when a country is selected, all associated states are displayed. States that are not assigned to the selected “master” country are not shown. | ||
| - | When a new state is entered, the correct foreign key is used automatically. The state is therefore assigned to the correct country. | + | When a new state is entered, the correct foreign key is used automatically. The state is, therefore, assigned to the correct country. |
| The master/detail relationship between districts and states is created between the foreign key (DISTRICTS.STAT_ID) and the primary key (STATES.ID). This means that when a state is selected, all associated districts are displayed. Districts that are not assigned to the selected “master” state are not shown. | The master/detail relationship between districts and states is created between the foreign key (DISTRICTS.STAT_ID) and the primary key (STATES.ID). This means that when a state is selected, all associated districts are displayed. Districts that are not assigned to the selected “master” state are not shown. | ||
| - | When a new district is entered, the correct state is used. The district is therefore automatically assigned to the correct state. | + | When a new district is entered, the correct state is used. The district is, therefore, automatically assigned to the correct state. |
| + | \\ | ||
| **<fs 20px>Note</fs>** | **<fs 20px>Note</fs>** | ||
| - | A master/detail relationship does NOT require that a foreign key relationship exists between two tables. Any columns can be used. | + | A master/detail relationship does NOT require that a foreign key relationship exist between two tables. Any columns can be used. |